2. The thing above all others desired or willed by an intellectual nature is the most perfect thing in that nature, and that is its happiness. But the most perfect thing in each is its most perfect activity: for power and habit are perfected by activity: hence the Philosopher says that happiness is a perfect activity.* Now the perfection of activity depends on four conditions. First, on its kind, that it be immanent in the agent. I call an activity 'immanent in the agent,' when nothing else comes of it besides the act itself: such are the acts of seeing and hearing: such acts are perfections of the agents whose acts they are, and may have a finality of their own in so far as they are not directed to the production of anything else as an end. On the other hand, any activity from which there results something done besides itself, is a perfection of the thing done, not of the doer: it stands in the relation of a means to an end, and therefore cannot be the happiness of an intellectual nature. Secondly, on the principle of activity, that it be an activity of the highest power: hence our happiness lies not in any activity of sense, but in an activity of intellect, perfected by habit. Thirdly, on the object of activity; and therefore our happiness consists in understanding the highest object of understanding. Fourthly, on the form of activity, that the action be perfect, easy, and agreeable. But the activity of God fulfils all these conditions: since it is (1) activity in the order of understanding; and (2) His understanding is the highest of faculties, not needing any habit to perfect it; and (3) His understanding is bent upon Himself, the highest of intelligible objects; and (4) He understands perfectly, without any difficulty, and with all delight. He is therefore happy.
3. Boethius says that happiness is a state made perfect by a gathering of all good things. But such is the divine perfection, which includes all perfection in one single view (Chapp. XXVIII, LIV).
4. He is happy, who is sufficient for himself and wants nothing. But God has no need of other things, seeing that His perfection depends on nothing external to Himself; and when He wills other things for Himself as for an end, it is not that He needs them, but only that this reference befits His goodness.
5. It is impossible for God to wish for anything impossible (Chap. LXXXIV). Again it is impossible for anything to come in to Him which as yet He has not, seeing that He is nowise in potentiality (Chap. XVI). Therefore He cannot wish to have what He has not: therefore He has whatever He wishes; and He wishes nothing evil (Chap. XCV). Therefore He is happy, according to the definition given by some, that "he is happy who has what he wishes and wishes nothing evil." His happiness the Holy Scriptures declare: Whom he will show in his own time, the blessed and powerful one (i Tim. vi, 15).
1.99 : That the Life of God is everlasting
1.101 : That God is His own Happiness