Summa Theologica, by St. Thomas Aquinas, [1947], at sacred-texts.com
After considering all that pertains to the unity of the divine essence, we come to treat of the divine beatitude. Concerning this, there are four points of inquiry:
(1) Whether beatitude belongs to God?
(2) In regard to what is God called blessed; does this regard His act of intellect?
(3) Whether He is essentially the beatitude of each of the blessed?
(4) Whether all other beatitude is included in the divine beatitude?
Objection 1: It seems that beatitude does not belong to God. For beatitude according to Boethius (De Consol. iv) "is a state made perfect by the aggregation of all good things." But the aggregation of goods has no place in God; nor has composition. Therefore beatitude does not belong to God.
Objection 2: Further, beatitude or happiness is the reward of virtue, according to the Philosopher (Ethic. i, 9). But reward does not apply to God; as neither does merit. Therefore neither does beatitude.
On the contrary, The Apostle says: "Which in His times He shall show, who is the Blessed and only Almighty, the King of Kings and Lord of Lords." (1 Tim. 6:15).
I answer that, Beatitude belongs to God in a very special manner. For nothing else is understood to be meant by the term beatitude than the perfect good of an intellectual nature; which is capable of knowing that it has a sufficiency of the good which it possesses, to which it is competent that good or ill may befall, and which can control its own actions. All of these things belong in a most excellent manner to God, namely, to be perfect, and to possess intelligence. Whence beatitude belongs to God in the highest degree.
Reply to Objection 1: Aggregation of good is in God, after the manner not of composition, but of simplicity; for those things which in creatures is manifold, pre-exist in God, as was said above (Q[4], A[2]; Q[13], A[4]), in simplicity and unity.
Reply to Objection 2: It belongs as an accident to beatitude or happiness to be the reward of virtue, so far as anyone attains to beatitude; even as to be the term of generation belongs accidentally to a being, so far as it passes from potentiality to act. As, then, God has being, though not begotten; so He has beatitude, although not acquired by merit.
Objection 1: It seems that God is not called blessed in respect to His intellect. For beatitude is the highest good. But good is said to be in God in regard to His essence, because good has reference to being which is according to essence, according to Boethius (De Hebdom.). Therefore beatitude also is said to be in God in regard to His essence, and not to His intellect.
Objection 2: Further, Beatitude implies the notion of end. Now the end is the object of the will, as also is the good. Therefore beatitude is said to be in God with reference to His will, and not with reference to His intellect.
On the contrary, Gregory says (Moral. xxxii, 7): "He is in glory, Who whilst He rejoices in Himself, needs not further praise." To be in glory, however, is the same as to be blessed. Therefore, since we enjoy God in respect to our intellect, because "vision is the whole of the reward," as Augustine says (De Civ. Dei xxii), it would seem that beatitude is said to be in God in respect of His intellect.
I answer that, Beatitude, as stated above (A[1]), is the perfect good of an intellectual nature. Thus it is that, as everything desires the perfection of its nature, intellectual nature desires naturally to be happy. Now that which is most perfect in any intellectual nature is the intellectual operation, by which in some sense it grasps everything. Whence the beatitude of every intellectual nature consists in understanding. Now in God, to be and to understand are one and the same thing; differing only in the manner of our understanding them. Beatitude must therefore be assigned to God in respect of His intellect; as also to the blessed, who are called blesses [beati] by reason of the assimilation to His beatitude.
Reply to Objection 1: This argument proves that beatitude belongs to God; not that beatitude pertains essentially to Him under the aspect of His essence; but rather under the aspect of His intellect.
Reply to Objection 2: Since beatitude is a good, it is the object of the will; now the object is understood as prior to the act of a power. Whence in our manner of understanding, divine beatitude precedes the act of the will at rest in it. This cannot be other than the act of the intellect; and thus beatitude is to be found in an act of the intellect.
Objection 1: It seems that God is the beatitude of each of the blessed. For God is the supreme good, as was said above (Q[6], AA[2],4). But it is quite impossible that there should be many supreme goods, as also is clear from what has been said above (Q[11], A[3]). Therefore, since it is of the essence of beatitude that it should be the supreme good, it seems that beatitude is nothing else but God Himself.
Objection 2: Further, beatitude is the last end of the rational nature. But to be the last end of the rational nature belongs only to God. Therefore the beatitude of every blessed is God alone.
On the contrary, The beatitude of one is greater than that of another, according to 1 Cor. 15:41: "Star differeth from star in glory." But nothing is greater than God. Therefore beatitude is something different from God.
I answer that, The beatitude of an intellectual nature consists in an act of the intellect. In this we may consider two things, namely, the object of the act, which is the thing understood; and the act itself which is to understand. If, then, beatitude be considered on the side of the object, God is the only beatitude; for everyone is blessed from this sole fact, that he understands God, in accordance with the saying of Augustine (Confess. v, 4): "Blessed is he who knoweth Thee, though he know nought else." But as regards the act of understanding, beatitude is a created thing in beatified creatures; but in God, even in this way, it is an uncreated thing.
Reply to Objection 1: Beatitude, as regards its object, is the supreme good absolutely, but as regards its act, in beatified creatures it is their supreme good, not absolutely, but in that kind of goods which a creature can participate.
Reply to Objection 2: End is twofold, namely, "objective" and "subjective," as the Philosopher says (Greater Ethics i, 3), namely, the "thing itself" and "its use." Thus to a miser the end is money, and its acquisition. Accordingly God is indeed the last end of a rational creature, as the thing itself; but created beatitude is the end, as the use, or rather fruition, of the thing.
Objection 1: It seems that the divine beatitude does not embrace all other beatitudes. For there are some false beatitudes. But nothing false can be in God. Therefore the divine beatitude does not embrace all other beatitudes.
Objection 2: Further, a certain beatitude, according to some, consists in things corporeal; as in pleasure, riches, and such like. Now none of these have to do with God, since He is incorporeal. Therefore His beatitude does not embrace all other beatitudes.
On the contrary, Beatitude is a certain perfection. But the divine perfection embraces all other perfection, as was shown above (Q[4], A[2] ). Therefore the divine beatitude embraces all other beatitudes.
I answer that, Whatever is desirable in whatsoever beatitude, whether true or false, pre-exists wholly and in a more eminent degree in the divine beatitude. As to contemplative happiness, God possesses a continual and most certain contemplation of Himself and of all things else; and as to that which is active, He has the governance of the whole universe. As to earthly happiness, which consists in delight, riches, power, dignity, and fame, according to Boethius (De Consol. iii, 10), He possesses joy in Himself and all things else for His delight; instead of riches He has that complete self-sufficiency, which is promised by riches; in place of power, He has omnipotence; for dignities, the government of all things; and in place of fame, He possesses the admiration of all creatures.
Reply to Objection 1: A particular kind of beatitude is false according as it falls short of the idea of true beatitude; and thus it is not in God. But whatever semblance it has, howsoever slight, of beatitude, the whole of it pre-exists in the divine beatitude.
Reply to Objection 2: The good that exists in things corporeal in a corporeal manner, is also in God, but in a spiritual manner.
We have now spoken enough concerning what pertains to the unity of the divine essence.