Genesis 1:3-5
Then God said, "Let there be light"; and there was light. 4And God saw the light, that it was good; and God divided the light from the darkness. 5God called the light Day, and the darkness He called Night. So the evening and the morning were the first day.
Matthew Henry: “4. [Observe] That God divided the light from the darkness. Yet he divided time between them, the day for light and the night for darkness, in a constant and regular succession to each other. Though the darkness was now scattered by the light, yet it takes its turn with the light, and has its place, because is 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 [calmness] of the night, and draw the curtains about us, that we may sleep the better.”
Clay Miller: First, nothing in Genesis 1 would give any indication that each day was anything more than a 24 hour cycle that we experience to this day. The only way anyone would come to this conclusion is if they were trying to force some kind of pet evolutionary theory onto the account. On the contrary, it clearly states there was evening and morning…a regular day. Added to that, any time a number precedes this term for day, it always reflects the regular solar day. This was the “first” day. And it does not matter that the sun was not created until the 4th day. Whatever the light was, it had its time in a regular cycle and three days later was replaced with the sun. God could have created all six days worth of work in a less than a nanosecond, but He had a purpose, part of which was to establish what the entire world recognizes as “the week”.
Second, In the same way physical light and darkness take turns and have their uses…so in the spiritual sense, or in life in general. God has His purpose for times of darkness in our lives. He uses afflictions, dark times, to teach us. I have often said that difficulties are Bible study…because many times our trials are exegeting Scripture (drawing the meaning out of texts). And then in another sense, light and darkness can illustrate productive times and restful times. Both have their place and both are needed faithfully.