And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.

Wesley's Notes

1:3-5 We have here a farther account of the first day's work. In which observe,
1. That the first of all visible beings which God created was light, the great beauty and blessing of the universe: like the first - born, it doth, of all visible beings, most resemble its great parent in purity and power, brightness and beneficence.
2. That the light was made by the word of God's power; He said, Let there be light - He willed it, and it was done; there was light - Such a copy as exactly answered the original idea in the eternal mind.
3. That the light which God willed, he approved of. God saw the light, that it was good - 'Twas exactly as he designed it; and it was fit to answer the end for which he designed it.
4. That God divided the light from the darkness - So put them asunder as they could never be joined together: and yet he divided time between them, the day for light, and the night for darkness, in a constant succession. Tho' the darkness was now scattered by the light, yet it has its place, because it has its use; for as the light of the morning befriends the business of the day, so the shadows of the evening befriend the repose of the night. God has thus divided between light and darkness, because he would daily mind us that this is a world of mixtures and changes. In heaven there is perpetual light, and no darkness; in hell utter darkness, and no light: but in this world they are counter - changed, and we pass daily from one to another; that we may learn to expect the like vicissitudes in the providence of God.
5. That God divided them from each other by distinguishing names. He called the light Day, and the darkness he called night - He gave them names as Lord of both. He is the Lord of time, and will be so 'till day and night shall come to an end, and the stream of time be swallowed up in the ocean of eternity.
6. That this was the first day's work, The evening and the morning were the first day - The darkness of the evening was before the light of the morning, that it might set it off, and make it shine the brighter.

King James Translators' Notes

And the evening...: Heb. And the evening was, and the morning was etc.

Scofield Reference Notes

[1] day

The word "day" is used in Scripture in three ways:

(1) that part of the solar day of twenty-four hours which is light Gen 1:5,14 Jn 9:4 11:9.

(2) such a day, set apart for some distinctive purpose, as, "day of atonement" (Lev 23.27); "day of judgment" Mt 10:15.

(3) a period of time, long or short, during which certain revealed purposes of God are to be accomplished, as "day of the Lord."

[2] evening

The use of "evening" and "morning" may be held to limit "day" to the solar day; but the frequent parabolic use of natural phenomena may warrant the conclusion that each creative "day" was a period of time marked off by a beginning and ending.

Jamieson-Fausset-Brown Bible Commentary

5. first day-a natural day, as the mention of its two parts clearly determines; and Moses reckons, according to Oriental usage, from sunset to sunset, saying not day and night as we do, but evening and morning.

Matthew Henry's Concise Commentary

1:3-5 God said, Let there be light; he willed it, and at once there was light. Oh, the power of the word of God! And in the new creation, the first thing that is wrought in the soul is light: the blessed Spirit works upon the will and affections by enlightening the understanding. Those who by sin were darkness, by grace become light in the Lord. Darkness would have been always upon fallen man, if the Son of God had not come and given us understanding, 1Jo 5:20. The light which God willed, he approved of. God divided the light from the darkness; for what fellowship has light with darkness? In heaven there is perfect light, and no darkness at all; in hell, utter darkness, and no gleam of light. The day and the night are the Lord's; let us use both to his honour, by working for him every day, and resting in him every night, meditating in his law both day and night.