Genesis 1:14-15  "And God said, Let (there's that word 'let' again) there be lights in the firmament of the heaven to divide the day from the night; and let (let) them be for signs and for seasons, and for days, and years; And let (let) them be for lights in the firmament of the heaven to give light upon the earth: and it was so.

There are three more verses on this subject of 'lights'. (vs. 16-18) This is the longest passage on any subject so far. Lights in the firmament.  The heavenly expanse.  I've always wondered why this was so important to God that he gave five verses on this subject and nothing on dinosaurs.  Or on the life forms in the water, or on what happened in the verses between vs. 1 and vs. 2.  But He didn't.

Perhaps, as we get ready for man to appear in this story, the lights in the firmament were a mystery that spoke of God;  He speaks of Himself through the universe.  "The heavens declare the glory of God; and the firmament sheweth his handwork.  Day unto day uttereth speech, and night unto night sheweth knowledge.  There is no speech, nor language, where their voice is not heard."  Psalms 19:1-3.