By Rabbi Jonny Hughes, October 14, 2014
The Torah teaches here that the sun and the moon have two distinct functions. The first is to differentiate between different times and seasons, a kind of celestial luach (calendar). The second is to illuminate the planet. Rashi understands that these two purposes are listed in order of importance.
The revered pre-War thinker, Rabbi Elchonon Wasserman, questions the order.