Genesis 1:3

We have here a further account of the first day's work, in which observe, 1. That the first of all visible beings which God created was light; not that by it he himself might see to work (for the darkness and light are both alike to him), but that by it we might see his works and his glory in them, and might work our works while it is day. The works of Satan and his servants are works of darkness; but he that doeth truth, and doeth good, cometh to the light, and coveteth it, that his deeds may be made manifest, Joh 3:21. Light is the great beauty and blessing of the universe. Like the first-born, it does, of all visible beings, most resemble its great Parent in purity and power, brightness and beneficence; it is of great affinity with a spirit, and is next to it; though by it we see other things, and are sure that it is, yet we know not its nature, nor can describe what it is, or by what way the light is parted, Job 38:19, Job 38:24. By the sight of it let us be led to, and assisted in, the believing contemplation of him who is light, infinite and eternal light (Jo1 1:5), and the Father of lights (Jam 1:17), and who dwells in inaccessible light, Ti1 6:16.

— Matthew Henry's Concise Commentary (public domain)

THE FIRST DAY. (Gen 1:3-5) God said--This phrase, which occurs so repeatedly in the account means: willed, decreed, appointed; and the determining will of God was followed in every instance by an immediate result. Whether the sun was created at the same time with, or long before, the earth, the dense accumulation of fogs and vapors which enveloped the chaos had covered the globe with a settled gloom. But by the command of God, light was rendered visible; the thick murky clouds were dispersed, broken, or rarefied, and light diffused over the expanse of waters. The effect is described in the name "day," which in Hebrew signifies "warmth," "heat"; while the name "night" signifies a "rolling up," as night wraps all things in a shady mantle.

— Jamieson-Fausset-Brown Commentary (public domain)