Genesis 1:16 NASB

In the sun and moon we find a divine lesson. Two lights on to govern. One to govern the day the other the darkness. But only one of them gives light. The other merely a reflection of the other. God is the source of all divine light. He is the source of goodness and truth his followers are to reflect that light. When the light of God can not be seen directly those who follow him are to be the reflection of that light. Here before the fall God creates a pattern for us to follow when the world falls into darkness.