The following by Dennis Isaacson is shared with permission:
“What is dividing the light and darkness about? We know that the creation of our sun and moon hadn’t been mentioned yet when this occurred, so what is this referring to? Let’s examine this:
“And the earth was without form, and void; and I caused darkness to come up upon the face of the deep; and my Spirit moved upon the face of the water; for I am God.
And I, God, said: Let there be light; and there was light.
And I, God, saw the light; and that light was good. And I, God, divided the blight from the darkness.” — Moses 2:2-4
Before we jump right in an attempt to analyze this, let’s also show what the Book of Abraham has to say about this same part of the creation account:
“And the earth, after it was formed, was empty and desolate, because they had not formed anything but the earth; and darkness reigned upon the face of the deep, and the Spirit of the Gods was brooding upon the face of the waters.
And they (the Gods) said: Let there be light; and there was light.
And they (the Gods) comprehended the light, for it was bright; and they divided the light, or caused it to be divided, from the darkness.” — Abraham 4:2-4
So the Mosaic account makes us think that the earth was without form, but the Abrahamic account shows us the the earth did have form (a sphere).
We would know nothing about what the light and darkness meant if it wasn’t for revealed knowledge about Satan rebelling against God and being cast down to earth.
I think there is merit in the idea that Satan and his hosts were here and that the darkness mentioned referred to them. Also, the “let there be light” command could be a calling together of the hosts that were with the Savior to assist in organizing the world. Therefore, the division of the light and darkness could be casting out Satan from the Heavenly host. Satan on one side (or in another realm) of earth oblivious to what was happening on the other side by Christ and his assistants.
BTW, I love the fact that both accounts mention the earth as having waters upon its surface. The earth as a hydro-planet is scriptural, whereas, the earth as a magma-planet is without mention.”