6 Such being the different senses of the word beginning, see if we have not all the meanings here. You may know the epoch when the formation of this world began, it, ascending into the past, you endeavour to discover the first day. You will thus find what was the first movement of time; then that the creation of the heavens and of the earth were like the foundation and the groundwork, and afterwards that an intelligent reason, as the word beginning indicates, presided in the order of visible things. You will finally discover that the world was not conceived by chance and without reason, but for an useful end and for the great advantage of all beings, since it is really the school where reasonable souls exercise themselves, the training ground where they learn to know God; since by the sight of visible and sensible things the mind is led, as by a hand, to the contemplation of invisible things.
“For,” as the Apostle says, “the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made.” Perhaps these words “In the beginning God created” signify the rapid and imperceptible moment of creation. The beginning, in effect, is indivisible and instantaneous. The beginning of the road is not yet the road, and that of the house is not yet the house; so the beginning of time is not yet time and not even the least particle of it.
If some objector tell us that the beginning is a time, he ought then, as he knows well, to submit it to the division of time— a beginning, a middle and an end. Now it is ridiculous to imagine a beginning of a beginning. Further, if we divide the beginning into two, we make two instead of one, or rather make several, we really make an infinity, for all that which is divided is divisible to the infinite. Thus then, if it is said, “In the beginning God created,” it is to teach us that at the will of God the world arose in less than an instant, and it is to convey this meaning more clearly that other interpreters have said: “God made summarily” that is to say all at once and in a moment. But enough concerning the beginning, if only to put a few points out of many.
Source: Nine Homilies of Hexaemeron (New Advent)