I answer that, As stated above (Article [2]), a thing may belong to the contemplative life in two ways: principally, and secondarily, or dispositively. That which belongs principally to the contemplative life is the contemplation of the divine truth, because this contemplation is the end of the whole human life. Hence Augustine says (De Trin. i, 8) that "the contemplation of God is promised us as being the goal of all our actions and the everlasting perfection of our joys." This contemplation will be perfect in the life to come, when we shall see God face to face, wherefore it will make us perfectly happy: whereas now the contemplation of the divine truth is competent to us imperfectly, namely "through a glass" and "in a dark manner" (1 Cor. 13:12). Hence it bestows on us a certain inchoate beatitude, which begins now and will be continued in the life to come; wherefore the Philosopher (Ethic. x, 7) places man's ultimate happiness in the contemplation of the supreme intelligible good.
Since, however, God's effects show us the way to the contemplation of God Himself, according to Rm. 1:20, "The invisible things of God . . . are clearly seen, being understood by the things that are made," it follows that the contemplation of the divine effects also belongs to the contemplative life, inasmuch as man is guided thereby to the knowledge of God. Hence Augustine says (De Vera Relig. xxix) that "in the study of creatures we must not exercise an empty and futile curiosity, but should make them the stepping-stone to things unperishable and everlasting."
Accordingly it is clear from what has been said (Articles [1],2,3) that four things pertain, in a certain order, to the contemplative life; first, the moral virtues; secondly, other acts exclusive of contemplation; thirdly, contemplation of the divine effects; fourthly, the complement of all which is the contemplation of the divine truth itself.