God is not only Eternal; He is His own Eternity; for His Duration is His Existence; as His Essence is His Existence, so is His Eternity.  And God alone is Eternal, for He alone is Unchangeable.  Other things share in Eternity in much the same way as they share from Him, in their own degree, of durability, as things corruptible have a long life, and thus Scripture speaks of the “eternal hills.”  With some things, as the elements, this participation is held by the whole, and not according to the parts; others, like the Angels and the Blessed, participate, in a strict sense, by the substantial incorruptibility of their individual act; their happiness is in the Word, and their thoughts are not changeable.  Eternity differs from Age and from Time.  Eternity is without succession, which cannot be said of time; because the very notion of Time means before and after.  Age differs from Time, for as Eternity is the measure of permanent existence, and is without before or after, nor can it be in a way comparable to such a notion; indeed, as a thing recedes from permanence of existence it recedes from Eternity, so also Age is without before or after in itself, but may possibly be joined to them accidentally, hence its measure is that of the heavenly bodies, the existence of which is unchangeable, although this may be joined to change as regards place.  The Angels have a changeless existence, with liability to change as regards election, so far as pertains to their nature, thus being mutable as regards intelligence, affection, and place, and their measure of existence is Age.  But corruptible things that recede so far from permanence of existence as to be subject to change, like all movement, are measured by Time.

Age is one; for as the oneness of Time is derived from the unity of the first movement, which is the most simple, and the rule of measurement for all others, so one Age is the measure of all others, and the more it is simply the first the more simple it is, and the principle of the rest.  But many ages are reckoned as so many centuries. St Thomas Aquinas, A Compendium of the Summa

Whether “one” and “many” are opposed to each other? (See ST. 1a, Q. 11, art. 2)One is opposed to many, but in different ways, for one, which is the beginning of numbers, is opposed to multitude as the measure is to the thing measured, because One represents the first measure, and number is multitude measured by one, while One, as it is interchangeable with Being, is opposed to multitude by way of privation of multitude, as the undivided is to the divided.

Whether God is one? (See ST. 1a, Q. 11, art. 3)God is One, for that which causes a thing to be singular cannot be communicated to many; and this belongs to God, for God Himself is His own Nature; hence “God” and “this God” are the same. Wherefore there cannot be many gods, which is also evident from the fact that God comprehends in Himself the whole perfections of existence. If there were several gods, something would belong to one and not to another, and so he in whom was privation of anything would not be simply perfect. The same is likewise proved by the unity of the world, for one is the cause of one, and things are better arranged by one than by many, and are brought into a uniform order.  Whether God is pre-eminently one? (See ST. 1a, Q. 11, art. 4) Thus God is pre-eminently One, because He is pre-eminently Being, inasmuch as He has not an existence restricted to any other nature, but He is Himself His own Existing Essence, entirely indeterminate and absolutely undivided in act and potentiality, for He is in every way Simple. Hence God is pre-eminently One.

What is Eternity? ST Ia. 10, 1Eternity is defined by Boethius, interminabilis vitae tota simul et perfecta possessio, “the perfect and simultaneous possession of interminable life.” We know what is simple by that which is composite; for we know first what is composite, through which we attain to the notion of simplicity.  Accordingly, Eternity becomes known to us in a twofold manner: first, as that which belongs to Eternity is interminable, without beginning or end; the term can be applied to both.  Secondly, this Eternity is without succession, it exists all at once.  Thus it exists always according to one and the same mode, the idea of before or after has no place in it at all.  God is Eternal ST Ia. 10, 2 God is Eternal because He is Unchangeable; thus Immutability belongs to Eternity, as movement belongs to time.

God is not only Eternal; He is His own Eternity; for His Duration is His Existence; as His Essence is His Existence, so is His Eternity.  Is God Alone Eternal? ST Ia. 10, 3And God alone is Eternal, for He alone is Unchangeable.  Other things share in Eternity in much the same way as they share from Him, in their own degree, of durability, as things corruptible have a long life, and thus Scripture speaks of the “eternal hills.”  With some things, as the elements, this participation is held by the whole, and not according to the parts; others, like the angels and the Blessed, participate, in a strict sense, by the substantial incorruptibility of their individual act; their happiness is in the Word, and their thoughts are not changeable.  Does Eternity Differ From Time? ST Ia. 10, 4 Eternity differs from Age and from Time.  Eternity is without succession, which cannot be said of Time; because the very notion of Time means before and after.  What Is the Difference Between Aeviternity and Time? ST Ia. 10, 5 Age differs from Time, for as Eternity is the measure of permanent existence, and is without before and after, nor can be in a way comparable to such a notion; indeed, as a thing recedes from permanence of existence it recedes from Eternity, so also Age is without before or after in itself, but may possibly be joined to them accidentally, hence its measure is that of the heavenly bodies, the existence of which is unchangeable, although this may be joined to to change as regards place.  The angels have a changeless existence, with liability to change as regards election, so far as pertains to their nature, thus being mutable as regards intelligence, affection, and place, and their measure of existence is Age.  But corruptible things that recede so far from permanence of existence as to be subject to change, or whose existence consists in change, like all movement, are measured by Time.

Is There Only One Aeviternity? ST Ia. 10, 6 Age is one; for, as the oneness of Time is derived from the unity of the first movement, what is the most simple, and the rule of measurement for all others, so one Age is the measure of all others, and the more it is simply the first the more simple it is, and the principle of the rest.  But many ages are reckoned as so many centuries.

For Further Reading:

Immutability

Nor is this intimate presence of God in the world to be mistaken for that tortured, twisting, developing god of the moderns that fights its way towards perfection through the struggle of the universe, changing as we change, getting better as we improve. God is altogether unchangeable. For what is change but the realization of a potentiality, the receiving of something new or the loss of something old. In God there can be no potentiality, nothing to be lost, nothing to be gained. He is pure actuality, pure being, possessing all things. He is beyond change and He alone; for He alone is first, dependent on no other, free of all potentiality.

To the modern philosopher this notion makes God completely static; if this be true, then this is a dull, stagnating, deteriorating God. His reason is not dissimilar from thc reasons for a New Yorker’s distaste for travel, an Englishman’s tolerance of the continent or an American tourist’s amusement at the strange antics of the rest of the world. In his own little world of creatures, the modern philosopher sees clearly that there must be change for progress, that immutability is closely akin to stagnation and deterioration. The point is that he is provincial enough to judge everything, even God, by the standards of that created world. It is true that change is inseparable from perfection in the world of unrealized potentialities; but it is also true that such a world is inconceivable without a Being of pure actuality, a Being Who is pure activity, Who has no potentiality, no possibility of losing or gaining but is a white flame of perfection. Such a Being is not in a state of static inertia; His is an activity so intense that change of any kind is impossible to it.- Walter Farrell A Companion To The Summa

Whether God is everywhere? (See ST Ia. 8, 2)God is said to be in every place by His Power, not as a body fills place, excluding every other by the fact of its being there, for, rather, God may be said to fill place, inasmuch as He gives to all things in place that which makes them to be in place. Thus God is present effectively in all created things, but objectively in the rational creature which knows and loves Him by act or habit; in such a manner is God present by grace in the saints.

Whether God is everywhere by essence, presence, and power? (See ST. Ia. 8, 3)Thus, therefore, He is present in all things by power, inasmuch as all things are subject to Him; and He is in all things by His Presence, as all things are bare and open to His eyes; and He is in all things by His Essence, inasmuch as He is in all as the Cause of Being. Moreover, (ST. Ia. 8, 4) that is properly said to be everywhere which is necessarily present in any given place, which is proper to God; for however many places there might be, from their very existence it would follow that God must be in them all, for nothing can exist but by Him. Thus it belongs to God to be everywhere first and of Himself; and it belongs to Him alone that, however many places there might be, in each of them He must be present, not by division of parts, but wholly as He is in Himself.

From A COMPANION TO THE SUMMA by Walter Farrell:

Infinity

No limits are to be placed on the goodness of God, as no limits are to be assigned to any other divine attribute. How can you have a fence with nothing, absolutely nothing, on the other side of it? What is there of reality, that God will not have, to mark the spot where the fence must begin? Limitation is essentially a declaration of potentialities achieved or potentialities capable of achievement; without potentiality limitation is a contradiction in terms. And there can be no potentiality in God, for potentiality is a declaration of dependence. God has not received existence within the limits of a human, an animal or an angelic nature; He has not received at all, He is. The idea of reception is the idea of change, of potentiality actualized, of perfection within limits–something that our proof for His existence forced us to exclude from God. He is infinite, and He alone; for He alone is first, receiving from no one, giving to all.

Ubiquity

In a very real sense, this utterly limitless God overflows the limits of the universe. He is everywhere within it, yet not contained by it. Everything in the universe comes from God; existence is His proper effect. Where anything exists,\ there is God. Understand, now, this is not merely a matter of God first giving existence and then abandoning the universe to its fate; He does not give us a pat on the back as we leave the corner of nothingness to jump into the ring of life, leaving us to take the blows while He shouts advice that takes none of the sting out of the blows. Existence belongs to God; as long as existence endures, there is the hand of God sustaining it as a mother supports her infant or the throat of a singer sustains his song. God is everywhere, and only God; for only God is the infinite, the first cause explaining every existent thing.

The ubiquity of God, in common with all the divine perfections, is not a cold, abstract thing meaningless to men. Its significance for human living is inexhaustible. In thc concrete, it means, for instance, that God is in the surge of the sea, the quiet peace of hills and valleys, the cool refreshment of rain, the hard drive of wind-driven snow. In the cities He is in the bustling of crowds, the roar of traffic, the struggle for pleasure, for life, for happiness, in the majesty of towering buildings. In homes He is not to be excluded from the tired, drowsy hours of night, the hurried activity of morning, from the love and quarrels, the secret worries and unquestioning devotion, the sacrifice and peace that saturate a home. In every individual one of us God is more intimately present than we are to ourselves. Every existing thing within us demands not only the existence of God but also His constant presence, from every rush of blood from our hearts to every wish, every thought, every act. In other words, everything that is real must have God there as the explanation, the foundation, the cause of every moment of its reality.

Thomas puts this all succinctly and beautifully when he says that God is in the world, in everything and everyone in the world, by His essence, causing all things, by His presence, all things being naked and open to the eye of this intelligent cause, by His power on which everything depends, to which everything is subject.

There is in this conception a majesty that transforms the earth. The mistaken exaggerations of Eastern philosophy made men walk carefully lest, treading on a living thing, they tread on the soul of a man. We have no fear of treading on the soul of man nor on God; but we do live in a world vibrant with divinity. We can give a real reverence to every being because within it, supporting its very existence, is the living God Himself. There is terror in this conception, the terror of moving in an atmosphere pervaded with divinity, of being ourselves wrapped about with divinity, penetrated with the infinite. But there is also courage and comfort here to be had from no other source. We bar the world in general from everything but the surface of our lives; friends are allowed to enter a few rooms of our palace; love throws open the gates as far as it is given us to open them–as wide as physical signs or clumsy, stumbling, inadequate words can open our souls, as wide as sacrifice and devotion can keep those gates open. Only God can walk freely about the innermost corridors of our being. And He does. Unless He be there, we could not be.

The pessimistic pantheism of the East, to which our modern philosophy edges closer every day, distorted the truth of the intimate presence of God to the point of identifying everything with divinity. On such premises there was good grounds for pessimism. All distortions are false, this one is as absurdly false as the identification of my image in a mirror with myself or the inability to see any difference between the poet and his poem. None of the things created by God are divine; rather they are the mirrors of divinity, the effects of the divine cause that depend every instant on that cause for their reality

ST IA, Q. 7, 1 God is Infinite because His Immensity is not bounded by matter. The Divine Being is not contained in anything, but He is His own Self-Existence, and hence He is Infinite and Perfect. ST Ia, 7, 2 There is nothing absolutely infinite but God, although relatively it may be so. With regard to infinity as applied to matter, it is evident that everything in existence must have some form; thus its matter is determined by form and cannot be infinite, properly speaking; but in so far as matter remains in potentiality to an infinitude of forms, it is accounted relatively infinite. If we speak of infinity as applied to form, it is evident that those forms which are actually united to matter are finite; but the created forms independent of matter, as the opinion is regarding the angels, these would be relatively infinite as not limited by matter; but, however, because they are limited by a determinate nature, they cannot be, [properly speaking, infinite; and, therefore, God alone is absolutely infinite.

ST Ia, 7, 3 No natural body can be infinite in magnitude, because every natural body has a determinate substantial form to which belong fixed accidents; hence a body has a determinate quantity of more or less, which makes it impossible for it to be infinite. The same is evident if we consider motion. Every body has some movement, whereas an infinite body could have none; neither straight, for nothing can so move except outside its own place, which could not exist at all were it infinite; nor circular, because such a movement requires that one part be transferred to the place hitherto occupied by another part, and this could not be in an infinite circular body, for the lines radiating from the center become more distant from each other as they are more and more drawn out; if, therefore, a body were infinite, such lines would become infinitely distant from each other, and one could never get near the other.

ST Ia, 7, 4 It is likewise impossible for an infinite multitude to exist. A multitude exists according to some kind of multitude, and kind exists according the species of numbers; and no species of number is infinite, for number is multitude cannot be, either directly or accidentally. There can be, however, an infinite multitude in potentially, because increase of multitude follows upon division of multitude, and the more a thing is divided the greater will be the result in number. The infinity of being is thus found in potentiality, by the division of that which is continuous; and a like idea of infinity is also found in the addition of multitude.

From Walter Farrell’s Companion of the Summa:

No limits are to be placed on the goodness of God, as no limits are to be assigned to any other divine attribute. How can you have a fence with nothing, absolutely nothing, on the other side of it? What is there of reality, that God will not have, to mark the spot where the fence must begin? Limitation is essentially a declaration of potentialities achieved or potentialities capable of achievement; without potentiality limitation is a contradiction in terms. And there can be no potentiality in God, for potentiality is a declaration of dependence. God has not received existence within the limits of a human, an animal or an angelic nature; He has not received at all, He is. The idea of reception is the idea of change, of potentiality actualized, of perfection within limits–something that our proof for His existence forced us to exclude from God. He is infinite, and He alone; for He alone is first, receiving from no one, giving to all. (Source)

ST I, 5, 3 Whether every being is good?
ST I, 5, 4 Whether goodness has the aspect of final cause? Every being, as such is good, for being is actuality, which is a perfection, and this again is desirable and good in our idea of it, and hence everything is good; and good is a final cause for the reason because that which is first in the cause itself comes last in the thing which is caused; thus fire gives heat before it produces the nature of fire in its effects, although heat in the fire produces the substantial form. Hence in the process of causation we find, first, good, and the end which moves the efficient cause; secondly, the act of the efficient cause to the form; thirdly, there comes the form; and hence the contrary must be the case in the effect caused; for first is the form which makes it a being; secondly, the effective power which makes it perfect in being, because each thing is perfect accordingly as it can produce its likeness; thirdly, comes the idea of goodness which makes a thing perfect.

ST I, 5, 5 Whether the essence of goodness consists in mode, species and order?
ST I, 5, 6 Whether goodness is rightly divided into the virtuous (just), the useful and the pleasant ( delectable)? The idea of Good is expressed in Mode, Species, and Order. The form makes everything what it is, and this presupposes antecedent and consequent principles, as, for instance, determination to one form or commensuration of its principles, whether material or efficient; and this is signified by mode; hence it is said that measure fixes the mode. The species is signified in the form because each thing is constituted in a species by the form, and tendency to the end or to action follows from the form. Further, each thing acts so far as it is in actuality and tends to that which belongs to it according to its form; and this belongs to order. hence the idea of Good implying perfection consists in mode, species, and order. So Good is properly divided into the useful, the just and the delectable. That which is desirable and terminates the movement of desire as the means wherey it tends to something else, is called useful; that which is desired as an end so as to entirely terminate desire and is desired for its own sake, is called just; and that which, being desired for its own sake, terminates desire by rest in the desired thing, is called delectable. Good is thus properly divided into these three.

S t Thomas doesn’t deal with this subject in the SCG in isolation but in relation to God. the SCG Book One, Chapter 37 can, however, be read at this point.

ST I, 3, 1 Whether God is a body? God is not corporeal; first, because movement is not possible to a body except by an external agent-God is the First cause of motion, Himself being immovable, as was shown above; secondly, a body is a potentiality (in potentia) because, as it is continuous, it is divisible indefinitely, whereas God is the noblest of all Beings in Act; and, therefore, cannot be corporeal, a body being either living or not living, and a living body is nobler than a not living body; but a living body does not live as such, otherwise every body would live, and so it must live y another, which is the soul. That which gives life to the body is nobler than the body. It is, therefore, impossible that God should be corporeal. (See SCG 1, 16 and 1,20)
ST I, 3, 2 Whether God is composed of matter and form? (See SCG 1, 17, 1, 18, )
ST I, 3, 3 Is there composition of quiddity, essence, or nature, and subject in Him? (See SCG 1, 21)
ST I, 3, 4 Is He composed of essence and existence? (See SCG 1, 22)
God is not composed of matter and form. Matter is of itself a potentiality. God is True Actuality, having no potentiality. Further, every created being is good and perfect by virtue of its form and by participation, as matter participates form; but as God is the first and highest Good, He is not Good y participation, but by His own Essence; therefore He is no composite. It is clear also, from being the First Efficient Cause, an therefore, the First Cause and acting of Himself, and Form by His own Essence, why He is not composed of matter and form. God is identified with His Essence or Nature, whereas in single forms which are their own individuality the subject is the same as the nature; therefore, God is His own Deity and His own Life, and all else that can be predicated of Him. In things composed of matter and form nature differs from the subject, because the nature or essence comprehends in itself only what falls under the definition of Species, and so it does not comprehend the individualizing matter, and thereby it is distinguished from the subject. So God is not only His own Essence, but His own Existence; for whatever is in anything besides its essence must be caused either by the essence or by some external agent; but it cannot be by the essence alone, for to e its own cause of being is beyond any being. If this is caused by an external agent, it must be as regards anything that has existence and essence distinct, that it should have a cause other than itself; but with God that cannot be, for He is, we have seen, the First Efficient Cause. Further, existence when distinct from essence is related to it as act to potentiality; but God is Pure Act with not potentiality, and, therefore, He is identified with His Essence; this is evident likewise from the fact that He is the First Being, and, therefore, must Be. If His Existence and Essence were not the same, he would Be by participation, and thus He would not the First Being; which is absurd to say of God.
ST I, 3, 5 Whether God is contained in a genus? Neither is God, properly speaking, in any genus. Species is made of genus and difference; and that from which difference comes stands towards that which makes the genus actual to the potential (thus the rational may be compared to the sensitive, as the actual to the potential, and so on); bus since in God the potential cannot be added to His Actuality, it cannot be that He should be as a species in a genus. Moreover, if God were in a genus, it must be that of Being, for genus signifies the essence of a thing, as when we predicate of a thing that is is such; but Being cannot be a genus, as Aristotle says, because every genus has differences external to its essence, whereas no difference can e external to a simple being. Therefore, God is not in a genus, for outside of Being there is only not-Being, which cannot be the difference among beings. Besides, all the members of one genus have those things in common which constitute the genus in its essence (of which it may be predicated that it is such), but they differ in their being; thus the being of a man is not the same as that of a horse, nor is the being of one man the same as another’s. There is a necessary difference, therefore between being (or existence) and essence in things which are in a genus; whereas the contrary has been proved in God, and, therefore, He is not in a genus. Neither does He belong to a genus by reduction to first principles, for whatever belongs to a genus by reduction does not extend beyond it; whereas God is the First Principle of all Being, and hence He cannot be contained as the first principle in any particular genus. (See SCG 1, 25)
ST I, 3, 6 Whether in God there are any accidents? Nor can there be any accident in God. The subject is to the accident as the potential is to the actual, and God being Pure Actuality, the potential has no place in Him. Then, as God is His own Existence, there can be nothing added to His Nature; just as heat has only heat, although a thing which is hot may have something external added to the heat, such as whiteness. Thirdly, whatever exists of itself is prior to that which is accidental. Hence, as God is the First Being, there cannot be in Him anything accidental. (See SCG 1, 23)
ST I, 3, 7 Whether God is wholly simple? God is, therefore, wholly Simple, for in Him there is no composition nor quantitative parts, neither is his Nature distinct from His Subject. he is wholly Simple likewise because what is composite comes after its component parts, and depends upon them; whereas God is the First Being. Moreover, a thing composite has a cause for its unity; But God has no cause, being Himself the First Efficient Cause. Also, in everything which is composite there is potentiality and acutality, which have no place in God. Finally, everything which is composite is a whole separate from its parts, whether like or unlike, which can in no way be said of God, Who is His own Form, or rather His own Form, or rather His own Being, and, therefore, is wholly Simple.

ST I, 3, 8 Whether God enters into the composition of other things? Neither does God enter into the composition of any other things, as some have erroneously thought ans said that He was the soul of the first heavens, or the formal principle of all things, or primal matter (materia prima), for God is the First Efficient Cause, and such cause is numerically distinct from the form of the effect, and only agree with it in species, as in the case of man generating a man. Matter does not agree with its efficient cause either numerically or specifically, for it is in potentia, and the latter is in actu. God, as the First Cause, is the highest, and acts by His own power; and so He is not a part of anything else. Nor can any part of a composite thing be the absolute first among beings, as God is; not matter or form, which are the principles of anything composite; for matter, which is potentiality, is simply posterior to actuality, and form, which is part likewise, is participated form which comes after that which is For by Essence. Therefore God does not enter into composition at all. (See SCG 1, 26 and 1, 27)

From A COMPANION TO THE SUMMA by Walter Farrell:

The most obvious implication from the proofs for the existence of God is that God is in no sense a composite or complex being; He is wholly simple. Before going on to establish the obvious character of this divine attribute of simplicity, it might be well to admit frankly that we have done such strange, contradictory things to simplicity that God might consider this particular attribute a dubious compliment. There is a great difference between the simple things we pity or patronize for their simplicity and the simple things to which we pay the tribute of profound respect and admiration. A simple-minded man is one who, through lack of ability or opportunity, does not know any better; whereas a richly simple gown is the result of supreme ability and unlimited opportunities. The simplicity of the child’s essay is altogether different from thc simplicity of the literary craftsman’s easy grace with words. In the one case we see simplicity as the mark of imperfection, in the other, as the stamp of genius; in both cases we are right, but it must be seen that we are using the word simple in decidedly different senses.

Simplicity is a badge of imperfection and will remain so in the world of created things where perfection must be measured in terms of potentialities and their realization. Man stands at the peak of the physical universe precisely because of his rich potentialities; his life is richer, fuller, as more of those potentialities are realized, as even greater potentialities are acquired, in a word, in proportion to the increased complexity of his life. He may cast an envious glance at a cat sleeping in a sunny window; life is so simple for a cat. But the envy is not real; no man wants to spend his life curled up in sleep. particularly in a window.

Yet this rich potentiality, the very basis of the complexity which makes up the perfection of created things, is itself a statement of imperfection. It implies imperfection; it is a declaration that something can still be had, that there is a void still to be filled up by some one some thing else. The being who has no potentialities, but only pure actuality, who is the source of all potentiality, alone escapes the stigma of imperfection and is free of the basic element of complexity. This being is utterly, completely simple; this is the being who receives nothing but gives all things. The simplicity we so admire and respect in created things, the simplicity that smacks of genius, is not really simplicity at all but the appearance of simplicity; men have succeeded in giving to rich complexity a smooth unity by a perfect coordination to a single end and we salute the faint image of divinity thus produced.

To say that God is simple means, in the concrete, that He is in no sense composite. He is not, has not, a body; He is not a golden calf or a painted idol. He has not divinity as man has humanity; He is divinity. His nature is not a cup filled to overflowing with existence, He is not full of life; He is existence, He is life. There are no family quarrels of the gods; there is nothing in God upon which to base a difference in divine nature. He does not grow fat or thin or red in the face; His thought is not a procession of concepts as is ours, for there is nothing accidental, transient, unessential in God. Because He is simple He cannot enter into composition with others as sugar does with coffee or oxygen with hydrogen; He cannot be immersed in the inert mass of matter like Bergson’s élan vital, expending His divine life fighting free with all the agony of a boy fighting his way out of sleep. God is simple because He is the first the completely independent source of all being.

Goodness and being are the same in substance but different according to our mode of conception; for Goodness implies the notion of desirerability, whereas Being is not necessarily bound up with anything of that kind. Nevertheless, as everything is good and perfect according to its actuality, a thing is good in proportion to its measure of being, which is actuality, and hence Goodness and Being are substantially the same. Being, however, is prior to Goodness in our conception of them, because a thing is knowable accordingly as it is actual; and, therefore, since Being is the proper object of the intellect, it falls under knowledge, and is thus prior to Goodness.

Every being, as such, is good, for being is actuality, which is a perfection, and this again is desirable and good in our idea of it, and hence everything is good; and good is a final cause because it is desirable. What is desirable is a final cause for the reason because that which is the first in the cause itself comes last in the thing which is caused; thus fire gives heat before it produces the nature of fire in its effect, although heat in the fire produces the substantial form. Hence in the process of causation we find, first, good, and the end which moves the efficient cause; secondly, the act of the efficient cause to form; thirdly, there comes the form; and hence the contrary must be the case in the effect caused; for the first is the form which makes it a being; secondly, the effective power which makes it perfect in being, because each thing is perfect accordingly as it can produce its likeness; thirdly, comes the idea of goodness which makes a thing perfect.

The idea of Good is expressed in Mode, Species, and Order. The form makes everything what it is, and this presupposes antecedent and consequent principles, as, for instance, determination to one form or commensuration of its principles, whether material or efficient; and this is signified by mode; hence it is said that measure fixes the mode. The species is signified in the form because each thing is constituted in a species by the form, and tendency to the end or to action follows from the form. Further, each thing acts so far as it is in actuality and tends to that which belongs to it according to its form; and this belongs to order. Hence the idea of Good implying perfection consists in mode, species, and order. So Good is properly divided into the useful, the just and the delectable. That which is desirable and terminates the movement of desire as the means whereby it tends to something else, is called useful; that which is desired as an end so as to entirely terminate desire and is desired for its own sake, is called just; and that which, being desired for its own sake, terminates desire by rest in the desired thing, is called delectable. Good is thus properly divided into these three.

Because the Master of Catholic Truth ought not only to teach the
proficient, but also to instruct beginners (according to the Apostle:
As Unto Little Ones in Christ, I Gave You Milk to Drink, Not Meat--
1 Cor. iii. 1, 2)--we purpose in this book to treat of whatever
belongs to the Christian Religion, in such a way as may tend to the
instruction of beginners. We have considered that students in this
Science have not seldom been hampered by what they have found written
by other authors, partly on account of the multiplication of useless
questions, articles, and arguments; partly also because those things
that are needful for them to know are not taught according to the
order of the subject-matter, but according as the plan of the book
might require, or the occasion of the argument offer; partly, too,
because frequent repetition brought weariness and confusion to the
minds of the readers.

Endeavoring to avoid these and other like faults, we shall try, by
God's help, to set forth whatever is included in this Sacred Science
as briefly and clearly as the matter itself may allow.

Companion to the Summa (hereafter CS):

Thomas, faced with the abundance of his material, did not hope merely
  to toss it before the minds of men; he expected to expose all this adequately,
  lucidly, and as briefly as the matter permitted. Moreover, he was not aiming
  at an increase in the intellectual jowls of the well cared for specialists
  in philosophy and theology; he had in mind, rather, the underfed, the starving,
  the little ones, beginners who had gone hungry too long. He expected to
  avoid all that would confuse the thinking of these little ones, that would
  impede their progress, that might contribute to their discouragement. The
  thing seemed important enough to this first professor of the age of Universities
  for an explicit statement of the instruments he had forged to bring it
  about: order above all, simplicity, and the ruthless elimination of useless
  questions, arguments and repetitions.

I, Q. 1, Art. 1 It is necessary for the salvation of man that, besides the natural sciences, there should exist some doctrine received by revelation; for many things are made known by revelation which transcends reason. Moreover, that which is discoverable about God by human reason could be known only to a few, and that after much time, and not without a large admixture of errors. It was good, therefore, for man to e taught by means of adoctrine divinely revealed; for salvation, which is in God, depends upon a knowledge of the truth.

The Division of the Book

The laziest man in the world might draw up a plan such as this. In fact, lazy men are usually prolific in their production of plans, perhaps the better to relish their idleness. The astonishing thing about Thomas’ project is that it came very close indeed to complete accomplishment, so close as to leave the onlookers breathless before the massive beauty of this intellectual cathedral, oblivious of its unfinished sacristy. Thomas’ project was stopped by the only thing that could stop it. He died while in the midst of his treatment of the sacrament of Penance.

The plan of the Summa is as simple as the statement of its aims by Thomas. The first part treats of God, both in Himself and as the principle from which the angelic, the human and the purely physical world take their rise; the second part treats of man’s movement back to the source from which he came; the third, of the means or the road which he travels to that goal and the home that waits for him at the end of the road.

It is the first part of the Summa which will occupy us throughout this volume. After a preliminary question (the burden of the rest of this chapter) we shall investigate the existence of the one God; then the inner life of the one true God, or the mystery of the Trinity; the rest of this volume will be taken up with a study of the angels, of men and of the world, for thus only can we have the full story of the procession of creatures from God. This latter part of the present volume will not involve argument about angels on the head of a pin; Thomas had no room for stupid questions. But it will involve the study and appreciation of all of the world, not merely the material part of it; of all of man, not merely the animal part of him; of all of the angelic world, not cynically amused caricatures of it. The pictures this study hangs in the minds of men will be strikingly different from those that today too often clutter the mind and shatter the heart. Man will not be found pictured here as a frightened god perched on the barren summit of a world in chaos. Nor will he be seen as no different in kind from the rest of the animals–his oddly human capacities for politics and poetry here are not only accidental differences which set him off from the beasts no more essentially than the fact that he is somewhat more fastidious about his bath. God will not have the hurried, harassed look of a timidly ineffective man; these angels will not be gliding around languidly looking for a holy card on which to alight. All these pictures have no inspiration in the world of reality; and it is only with reality that we are engaged in this volume.

It is extremely important, at the very outset, that we lay hold firmly on these two facts: Thomas, all his life, was a relentless searcher for reality, a ruthless enemy of falsehood; and his supreme work was a book of supernatural theology. In our own time, it has become the fashion to divorce theology from reason and so to destroy any certitude of its relation to reality. As for the supernatural, well that is an insult to our self-sufficiency not to be lightly suffered by an intelligent man. It is not too hard to understand the modern’s impatience with the supernatural, for man has always been proud; but only the intellectual suicide of positivism could be so absurd as to limit the horizons of a man’s mind to what he can uncover by the methods of science. This last has no need of rational refutation for the positivist contradicts himself in the denials that make up his doctrine; he advocates a way of death, rather than of life, for life cannot be lived on a basis of denials, it must be fled from. Men are intolerant of the cowardice of escape; they are sympathetic towards a spirit of independence, even exaggerated independence, though they, and everyone else, are barred from expressing that sympathy when the independence reaches the stage of voluntary confinement.

It is unquestionably true that man, left to his own devices, can gather a tremendous amount of information; so much, in fact, as to be smothered under the pile of facts he has heaped upon his own head. He can even, through the patient labor of the years, acquire something of wisdom’s understanding of the pattern of things, of the distinction between details and essentials, of goals and means to those goals. The point that is overlooked too often is that a man simply cannot wait so long for the advent of wisdom. He has to know these things from the beginning he has a human life to live through all the years that are demanded for the personal achievement of the long view of the wise man; and, for by far the greater number of men, the mind, the heart, the hands are well occupied in winning a livelihood from a grudging mother earth. To be quite frank, there are many men who will never arrive at wisdom under their own power if they live to be a hundred and have absolutely nothing to do but think. To be equally frank, it must be admitted that the wisest of men are going to make mistakes.

This matter of human goals that give the directions for human living is much too important to run such risks. This knowledge cannot wait, it cannot be restricted to a few, it cannot be punctuated by error; if we are content to have it so, it is only because we assume the unimportance of the human individual, the meaninglessness of human life, the certitude of long life, the indifference of truth. All of these assumptions are false. Because they are, man, even in those things that are not strictly above his human powers, must have help. He can assert his absolute independence only at the cost of compromising his knowledge of reality and, ultimately, at the cost of failure in the living of human life. He must accept truth from the source of truth; and be thankful the truth is given him.

Necessity of Wisdom

All this would be true if man’s life were to be fulfilled by a goal within the grasp of his natural powers. When we face the fact that the only goal of man is above all nature, the eternal vision of God, we see something of the desperate necessity for a divine revelation that will give him knowledge of that goal and the means by which he can arrive at it.

The illusion of independence can be bought at much too high a price. It could logically demand that we swim oceans rather than depend on a ship-builder and a navigator, that we toddle through blizzards naked until we can make our own clothes, that we fly by flapping our arms. Whatever the price paid, when we examine the thing in an honest light, the wonder is that we bought such a shoddy product at all; the certainty is that we have been badly cheated. There is nothing so completely useless as the illusion that we are self-sufficient, for there is nothing so completely false.

We must have wisdom from the beginning of life. It cannot be our own; nor is it sufficient if it is some other human being’s. It must be divine, for only God is wise from the beginning. To begin life with the wisdom lent us by divinity, and end it by possessing that wisdom; to meet the charges at each station of life with divinely minted coin; to see the road that stretches before us through the far seeing eyes of God — this is not an insult to human nature, it is an ennoblement of it.

I, Q. 1, Art. 2 This doctrine is a science proceeding from principles made known to us by the light of a higher science, as music proceeds from principles explained by arithmetic. For Sacred Doctrine proceeds from principles made known by the light of a higher knowledge, namely, the Divine Knowledge, and in it certain particulars are treated of, both as an example of life and in order that we may know clearly by what instrumentality this revelation is made.

A Divine Science — Its Object

In this atmosphere of nobility theology draws its first breath of life, for the deposit of divinely revealed truth constitutes the life principle of all theological science. If philosophy, as the apex of natural intellectual effort, has deserved the name of human wisdom, then theology is rightly called divine wisdom. All of its varied fabric is given solid substance by the thread of divinity that is woven into it; if we unravel that complex fabric, that single thread will always lead back to God, the source of truth and the goal of it. Without that thread of divinity theology is a name given to a crazy quilt that, paradoxically, is devoid not only of beauty but of variety, monotonous with the grey monotony of despair. It has nothing of wisdom about it, for it has nothing of meaning about it. But drawing its life-blood from the source of all order, theology is vibrant with such significance as man would not have dared to dream, with divine significance for creatures who hardly dare to face human life let alone dream of living divine life.

To speak of theology as a science may sound blasphemous to modern ears. Indeed, it is blasphemous if we restrict science to the treasure buried in the physical world, a treasure to be unearthed only by the pick-axe and spade of the experimental method. But if we take science, as it should be taken, in the larger sense of ripe knowledge plucked from principles that escape the blight of doubt, we can hardly mistake theology as a clever imitation of a live science, to be put under glass as a tribute not to its life but to its artificiality. We can, with an easy mind, expose it to the weather to live its rugged, vibrant life; let the rain fall on it and the wind tug at it, the sun shine on it and its enemies drag their tiny bodies over its broad branches. It will live; its roots are deep enough, its leaves broad enough, its branches high enough; it will live. though many a hybrid die beside it.

I, Q. 1, Art. 3 Sacred Doctrine takes account of all things only in so far as they belong to the formal order of Divine revelation. This science is one, neither wholly practical nor wholly speculative; but being of a higher order it includes both, yet remains one, as God knows both Himself and what He does with the same knowledge. It is, however, more speculative than piratical, for it treats more of Divine things than of human actions, being concerned with the latter only in so far as they are intended to lead man to the perfect knowledge of God, in which eternal beatitude consists.

Theology is no mongrel in the pack of sciences. Like every other science, it has its proper, and utterly distinctive, field–the field of revealable truths. Its paraphernalia is totally inadequate to furnish it with its principles: so, in common with all other sciences, it gets the principles with which it starts and on which it depends from some other source. The philosopher, with no human science above him, accepts without question the self-evident principles his reason discloses to him or he ceases to be a philosopher. The theologian accepts his principles, not from the science of the physicist, the mathematician or the philosopher, but from the science of God and the saints. No science proves its own principles; nor does theology. But the principles of every other science are susceptible, with the help of another science or directly from nature, of clear vision by the human mind; theology alone accepts principles too clear to be seen by any mind but the mind of God. It believes its principles on the authority of the Truth incapable of error or falsehood.

I, Q. 1, Art. 4 And this science is higher in dignity than other speculative sciences, for these derive their certainty from human reason, which may err, while Sacred Doctrine, owing to the light of Divine Knowledge, can never be deceived; moreover, they consider only things which are below reason, while she treats principally of such as transcend reason. Sacred Doctrine is also higher in dignity than other practical sciences, for, among such, that science is accounted the more honorable which is not subordinated to a further end, as military science is to civil; but the end of this doctrine, in as far as it is practical, is eternal beatitude, to which all other ends of the practical sciences are subordinate.

Let us suppose that all the sciences, in person, were invited to dinner by a great university. Where should theology be seated, among the practical or the speculative sciences? Well, the thing is more practical than domestic economy for it deals with the most practical of things the goal of a man and the roads to the goal; at the same time it is more speculative than metaphysics for it handles truths that are divine. It might take the grapefruit with the speculative sciences, move over to an empty chair for the soup with the practical sciences, back to its original place for the fish, and so on; a little fatiguing, perhaps, but then what can be done? Like many another person with an insoluble problem, the hostess will shelve it and pretend it does not exist, for the moment anyhow. Now about places, who will get the first place and who will slide humbly into the welcome obscurity of the seat far down the table? In the speculative section the question will have to be settled on the certitude of the science and the nobility of its subject matter. Theology jumps down from that mental shelf to worry the hostess: it would be hard to find a more noble subject matter than divinity or to compare the certitude achieved by a human mind to the certitude of the divine word. But the method! Yes, the others may be a little uppish on the question of method, but then how can we make a particular method the norm of precedence; is this a scientific dinner or a meeting of a secret society?

I, Q. 1, Art. 5 Also I, Q. 1, 7 And since it treats most properly of God as the First Cause, it is wisdom in the highest sense; for he is accounted wise in any department of knowledge who studies the highest cause in that department. Seeing, therefore, that Sacred Doctrine determines concerning God, not only as he may be known by creatures, but also as He is known by Himself alone, and by others through revelation, it is properly called wisdom in the highest sense, and God is the subject of it, for all things are considered with reference to Him, all things being related to Him either as their beginning or their end.

Very well, give theology the first place among the speculative sciences; at least that settles the question of where theology will sit. In the practical section, precedence will be determined by the ultimateness of the end served by the particular science. Obviously medicine will sit above domestic economy, but does it go above or below politics? We can settle that later; what is the very last end served by any science; theology again! The only solution is to sit theology in the very center with the speculative sciences descending on the right and the practical on the left, hoping, of course, that no wit brings up the matter of the sheep and the goats.

But enough of the dinner. Abandoning the figurative language and getting down to hard facts, it is true that the findings of the other sciences seem much more certain to us than the conclusions of theology. Of course; but the flame of an acetylene torch is not less bright because it blinds us, less visible because we must see it through smoked glasses; nor is the divine truth less certain because it is too clear for our eyes, it is not less sure because we have to see it through the obscure glass of faith. It is also true that theology uses philosophy; but that is not because the pillars of divine truth need so much bolstering, it is rather because of the comfort our weakness derives from the clasping hand of philosophy. But we shall come back to this matter of philosophy later on in this chapter.

For the theologian treats of nothing except in relation to the first beginning and the last end. He is in the intellectual order what the saint is in the practical order: a man wholly engaged with God. A general order covering the activity of the two men need suffer no single change in phrasing: “begin this task at once, work at it ceaselessly, finish it in eternity.” For the love of God is not to be encompassed in a lifetime; neither is the knowledge of God. However far afield the mind or the heart may seem to have wandered, both are engaged with God Himself or with the things that pertain to God as Beginning or as End. The saint knows the important answers by the quick intuition that has its deep roots in love; the theologian, by the reasoned argument that has its roots deep in study. When study and love are united to make a saint of a theologian, God has been exceptionally kind to men.

It is into the book of just such a man that we are timidly edging our way. There is a definite reassurance in the fact that Thomas insisted that reason roll up its sleeves and get down to its hardest task; this brings back the first day’s study of any science. Moreover he has adopted the fully developed form of that similar method of Socrates; and what is more familiar than a question? The double flattery of a question is hard to resist; the contentedly ignorant and the insufferably omniscient never ask a question, while the fool is asked a question only by mistake. A question, after all, is the movement of a mind in search of truth and there is nothing so pleasant to disseminate as truth. Children and scholars are living question marks and, as Thomas wrote for childish scholars, it was right that every article of his book be a question demanding a straight answer. To clarify the issue, an opponent, fictitious or real, is introduced each time with so forceful a presentation of objections as to cause a little anxiety in the heart of a follower of Thomas.

I, Q. 1, Art. 6 Also I, Q. 1, 8 Sacred Doctrine does not employ argument to prove its principles, which are articles of faith, but proceeds from them to demonstrate something else, as the Apostle argues from the resurrection of Christ to that of others. The inferior sciences, indeed, do not prove their first principles or argue with those who deny them, but leave them to be proved by a higher science, while metaphysics, which is the highest among them, only disputes with those who deny its first principles if the adversary grant something; if he grant nothing it cannot argue with him, but can still solve his objections. In like manner, Sacred Doctrine, having no superior, disputes with those who deny its principles provided the adversary grant something, and proceeds to argue from one article of faith against those who impugn others, as in the case of heretics. If, however, the adversary believe none of those things which are revealed, it is no longer possible to prove the articles of faith by reason alone, but only to solve objections brought against a faith which is rooted in infallible truth. For as it is impossible that what is contrary to truth can be proved to be true, the arguments brought against faith can be answered.

It is difficult to conjure up a picture of a rollicking theologian. Perhaps there have been such, but the odds are against it. Not that theology demands that its disciples all have long, white beards; but it does seem to demand that its youngest masters be old and its oldest masters be young. Perhaps all this is because of the bouquet that wisdom throws off as we warm the word in the hollow of our hands. We do associate wisdom with old age, not because the mind of the old is keener, the heart more eager, but because the tired feet have wandered enough to know the highroad from a bypath, the old eyes have seen enough, to know a trifle from the gem for which a man must sell all he has, because the old hands have worked at tasks enough to know the ephemeral from the enduring. Old age should know more of the answers, it should see more of the pattern, it should escape more of the confusion of the terrific detail of life. Theology is wisdom, old with the agelessness of eternity; but young with the youth of an eternal beginning.

The wise man to be consulted for the answers about the new house that is going up is the architect, not the bricklayer; if he does not know the reasons for things, there aren’t any. He may be stupid in many other lines, but in this one, because he is master of the ultimate purposes of the building, he is wise; in any line, this knowledge of ultimate purposes brings wisdom. When the knowledge is of the last of all purposes, it brings that wisdom that needs no qualification; by it a man is simply wise. This will be the man who knows the answers that really matter; these are the answers for, which the theologian exists.

The body of the articles throughout concentrates on the work of explaining, illustrating, persuading, refuting and, where possible, proving. Thomas, of course, does not argue about theology’s principles; no science does that. The inferior sciences depend on their superiors to take care of the borrowed principles; metaphysics, without a superior, will argue about its principles with an opponent who grants some of them; with an opponent who denies all of them it can do nothing but refute the denial, exposing its falsity. The procedure is the same in theology, with the added assurance that every objection in denial has its answer for these principles rest on the immutable truth of God.

But there is plenty of room for argument in theology beneath the principles; nor has there ever been a slackening of that argumentation that destroys error, preserves truth and uncovers still more of truth. Here philosophy is put to work in earnest; here human reason is employed to its fullest strength; for here is a task worthy of the great potentialities of the mind of a man. As a reward for this back-breaking labor, theology restricts the field of possible philosophical error, releasing this flood of conserved energy into the channels of real philosophical investigation. Philosophy is not substituted for, it is not destroyed, not diluted; for grace does not destroy nature, it perfects it. It is not superseded by a higher wisdom; it is consecrated by that higher wisdom.

I, Q. 1, Art. 9 I t benefits Sacred Doctrine to express things Spiritual and Divine by the use of corporeal metaphors, for God provides for every creature according to his nature, and men are led naturally by means of things sensible to knowledge which is purely intellectual. moreover, the Sacred Scriptures are for the instruction of all men, and the uncultured apprehend intellectual things more easily under corporeal similitudes.

I, Q. 1, Art. 10 And this Doctrine has several meanings under one letter. There is the literal, which is also called the historical sense, and the spiritual, when the things expressed in the words mean something else. The spiritual sense is threefold; for as the Old Law is the sign of the New, and the new Law is the figure of the future glory, there follows from this the allegorical sense. As they signify what makes up eternal glory, they give the anagogical sense. Since God is the author of this Doctrine, and he comprehends all things in the mind at once, it is most fitting that the one literal sense should contain many meanings.

For further reading: THE WISE MAN’S BOOK by Walter Farrell