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 Obj. 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 Obj. 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. _______________________
SECOND ARTICLE [I, Q. 26, Art. 2]
Whether God Is Called Blessed in Respect of His Intellect?
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.
Obj. 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. 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 blessed [beati] by reason of the assimilation to His beatitude.
Reply Obj. 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.