I have pointed out this subordination of practice to theory in Practical and Moral Essays, pp. 154, 155, cf. article 10, pp. 11-13.
St Thomas proceeds to instance three kinds of contemplation. (A) Intuition of first principles. This is enjoyed by every man, educated and uneducated, who has the ordinary use of reason. Needless to say, it is not happiness, or all men would be happy. (B) Scientific Knowledge, the property of the educated. But the objects of science are creatures; and man requires for his happiness to contemplate something higher and nobler. (C) Wisdom, which is defined (in B. I, Ch. I: "The knowledge of things by their highest causes." In this wisdom, taken for the contemplation of God, the beginning and last end of all, human happiness will be found to consist.
(A) is further suggestive of Chap. XXXVIII, in which it is shown that the plain man's rational knowledge of God is not happiness: while (B) and (C) together suggest Chap. XXXIX, which shows that the philosopher's knowledge of God is not happiness either. Chapter XL proves the same of the Christian's knowledge of God by faith. Chapter XLVII shows that we enjoy no vision of God on earth. Chapter XLVIII, that happiness is not on earth. Finally, Chap. L argues that nothing short of the immediate vision of God makes the happiness of angels and of human souls in heaven.
Of God and His Creatures: 3.37