Why the first day is called 'one' not 'first'

Or perhaps the more authoritative account is the one handed down in secret: that the God who fashioned the nature of time imposed measures and signs upon it—the intervals of days—and measuring it by the week, he commands the week always to return in a circle upon itself, counting out the movement of time. And the week, in turn, is completed by one day, returning upon itself seven times—and this is a circular shape, to begin from itself and end in itself. This is also the special property of eternity: to return upon itself and never come to an end. For this reason he named the head of time not “first day” but “one day,” so that even from the name it would have kinship with eternity. For the name that displays the character of what is solitary and unshared with another was fittingly and properly called “one.” And if Scripture presents many ages to us, speaking in many places of “age of age” and “ages of ages,” yet even there no first or second or third age has been counted out for us—so that from this we are shown differences of various conditions and affairs, not boundaries and limits and successions of ages. For “the day of the Lord,” it says, “is great and glorious” (Joel 2:11). And again, “Why do you seek the day of the Lord? It is darkness and not light” (Amos 5:18). Darkness, clearly, for those who deserve the darkness. For the word knows that day to be without evening, without succession, and without end—the day the psalmist also called the eighth, because it lies outside this sevenfold time. So whether you say “day” or “age,” you will mean the same thing. If that condition is called a day, it is one and not many; if it is called an age, it is solitary and not one of many. So to lead our thought toward the life to come, he named the image of eternity “one”—the firstfruits of days, the same age as the light, the holy Lord’s day, honored by the resurrection of the Lord. “And there was evening,” it says, “and there was morning, one day” (Genesis 1:5). But the words about that evening have been overtaken by the present evening, and here they bring our discourse to a close. May the Father of the true light, who adorned the day with heavenly light, who brightened the night with the rays of fire, who prepared the rest of the coming age with the spiritual and unceasing light, enlighten your hearts in the knowledge of the truth, and keep your life without stumbling, granting us to walk becomingly as in the day, so that you may shine like the sun in the brightness of the saints, for my boast, for the day of Christ—to whom be glory and power forever and ever. Amen.

HOMILY 3. On the Firmament.

The works of the first day—or rather, of the one day; for let us not take away from it the dignity it has in its nature, given by the Creator as a day in its own right, not numbered in sequence with the others—the things that came to be on it, then, our discourse went through yesterday and divided the explanation among the hearers, making the morning food for souls and the evening gladness. Now it moves on to the wonders of the second day.