Or HaChaim on Genesis 1:17/אור החיים על בראשית א׳:י״ז

1And He placed them: It did not suffice to say "and it was so," since it wanted to inform us that God gave this thing as a free present, to shine upon the world, as they, of blessed memory, have stated in the Midrash (Bereishit Rabbah 6:5); see there. And the intention with this is that they informed [us] that [the luminaries] do not shine upon the [inhabitants of the] world because they are deserving of light; for if so, all the time that the luminaries would see that the inhabitants of the earth were corrupting their ways, they would refrain [from giving] their light. Also by way of another reason, they would want to refrain [from giving] their light, as they have stated in the Midrash (Introduction to Eicah Rabbati) that Moshe, our teacher, of blessed memory, said to the sun during the destruction of the Temple, why did you not darken your light when the enemy entered the Temple, etc. For this [reason], God said that they are placed to shine upon the earth, and from now [on], they are not in their own control and are required in their actions to shine upon the earth and no reason can prevent [it]. And through this, they enlightened our eyes, [regarding] why the verse repeated to say "and to rule over the day" a second time - was it not already stated, "the great luminary for the rulership of the day, etc.?" And our Rabbis, of blessed memory, expounded (Bereishit Rabbah 6:9) that the verse is hinting to the righteous - see their words there - but according to the simple understanding, there is no reason to repeat and state [it]. And according to our approach, there is a need to repeat it and state it, [since] it states, "and He placed" [which can also be understood as "and He gave"], since 'they, they are given, they are given;' [meaning that] from now, behold, they are not in their own control and the obligation of others is upon them; for this [reason], it goes back and states that their rulership stands in its place, except that specifically concerning this aspect of brightening [the earth] only, it is not in their hands to deviate, but concerning the other [aspects of] rulership that were designated for them over the day and over the night, [about these] they are [still] the rulers.

2And the reason it repeats and again states, "and to separate," is that here He commanded them not to enter [past] the border of [the other] and each one is commanded not to trespass the border of the other, so that with this, day and night will be recognizable.