John Gill Commentary Genesis 1:15

"and let them be for lights in the firmament of heaven to give light upon the earth: and it was so." — Genesis 1:15 (ASV)

And let them be for lights in the firmament of the
heaven
To continue there as luminous bodies; as enlighteners, as the word signifies, causing light, or as being the instruments of conveying it, particularly to the earth, as follows: to give light upon the earth ;
and the inhabitants of it, when formed: and it was so :
these lights were formed and placed in the firmament of the heaven for such uses, and served such purposes as God willed and ordered they should.