Reason is absolutely assignable for the volitions of God regarding the universe: but relatively to us, we can assign it but vaguely, and, revelation apart, with much uncertainty. By aid of the Aristotelian and Ptolemaic cosmogonies, mediaeval writers had much to say of "the perfection of the universe," over which sayings the modern astronomer stands amazed, murmuring low to himself, if he is a pious man, Nimis profundae factae sunt cogitationes tuae (Ps. xci). A characteristic of the Middle Ages is idealisation of unity, permanence, and systematic completeness in the social, political, religious, and even in the cosmic order. To us "the perfection of the universe" is a less obvious ground of argument, There is such a perfection, doubtless, as the Creator is wise and good; and much of the wisdom and beauty of His work is manifest to our eyes; but the entirety is beyond us. We cannot comprehend it, as we cannot comprehend Him.
Of God and His Creatures: 1.86