Genesis 1:18

And to rule over the day, and over the night
The one, namely the sun, or greater light, to rule over the day, and the moon and stars, the lesser lights, to rule over the night: this is repeated from ( Genesis 1:16 ) to show the certainty of it, and that the proper uses of these lights might be observed, and that a just value might be put upon them, but not carried beyond due bounds: and to divide the light from the darkness;
as the day from the night, which is done by the sun, ( Genesis 1:14 ) and to dissipate and scatter the darkness of the night, and give some degree of light, though in a more feeble manner, which is done by the moon and stars: and God saw that [it was] good;
or foresaw it would be, that there should be such lights in the heaven, which would be exceeding beneficial to the inhabitants of the earth, as they find by good experience it is, and therefore have great reason to be thankful, and to adore the wisdom and goodness of God; see ( Psalms 136:1 Psalms 136:7-9 ) ( Ecclesiastes 11:7 ) . (See Gill on Genesis 1:4).