Charles Ellicott Commentary Genesis 1:4

"And God saw the light, that it was good: and God divided the light from the darkness." — Genesis 1:4 (ASV)

And God saw. — This contemplation indicates, first, a lapse of time; and second, that the judgment pronounced was the verdict of Divine reason.

That it was good. — As light was a necessary result of motion in the world-mass, so it was indispensable for all that was to follow, since neither vegetable nor animal life can exist without it. But the repeated approval by the Deity of each part and portion of this material universe also condemns all Manichaean theories, and asserts that this world is a noble home for humanity, and life a blessing, despite its solemn responsibilities.

And God divided ... — The first three creative days are all days of order and distribution, and have been called “the three separations.” But while on the first two days no new thing was created, but only the chaotic matter arranged, on the third day there was the introduction of vegetable life.

The division on the first day does not imply that darkness has a separate and independent existence, but that there were now periods of light and darkness. Thus, by the end of the first day, our earth must have advanced far on its way toward its present state (See Note, Genesis 1:5). It is, however, even more probable that the ultimate results of each creative word are summed up in the account given of it.

No sooner did motion begin than the separation of the air and water from the denser particles must have also begun. The immediate result was light; after a greater interval followed the formation of an open space around the contracting earth-ball; still more remotely came the formation of continents and oceans; but the separations must have commenced as soon as the “wind of Elohim” began to brood upon and move the chaotic mass.

How far these separations had advanced before there were recurrent periods of light and darkness is outside the scope of the Divine narrative, which is not geological but religious.