Halakhah su Salmi 104:19

"Who appointed the moon for seasons" (Psalms 104:19). R. Yoḥanan commented: The orb of the sun alone was created to give light. If so, why was the moon created? "For seasons": in order to sanctify new moons and years thereby. R. Shila of Kefar Temarta said in R. Yoẕanan's name: Yet even so, "the sun knows its coming" (Psalms 104:19): from the sun one knows the [month's] coming, for we count the beginning of the month only from sunset.

This concept also appears to be reflected in the words of Pesikta Rabbati 15:1. Citing the verse "Who appoints the moon for seasons; the sun knows its going down" (Psalms 104:19), Pesikta Rabbati comments, "Because 'the sun know its going down'—from here [it is derived] that we do not calculate according to the moon unless the sun has set." In context, Pesikta Rabbati declares that even though the nascent moon has been sighted a new month does not begin until the sun sets. The import of that statement would certainly seem to be that a new day can begin only upon the actual setting of the sun.¹⁹See Naḥalat Ya‘akov, no. 4.

And according to the plain meaning, the reason that we bless the moon more than the stars/planets, although it's smaller than almost all the other planets (excepting Mercury), is because it's closer to the Earth than all the other stars/planets; it's only about 43,000 parasangs away. The moon inspires in us a feeling of the greatness of the Holy Blessed One, since every night its path is perceived, and it orbits the earth every month. For this reason it's called "yareach" [ירח], as it is written "[God] made a moon [ירח] to mark the seasons" (Psalms 104:19) -- since it orbits the earth in every moon of days, and its waxing and waning are perceptible. And Israel, who count [days] by the moon, are compared to the moon; just as the moon has no light of its own, and is illuminated by the sun's light, so too Israel have no light other than the Light of the Holy Blessed One, which shines for us from the midst of the Holy Torah, as it is written "A sun and a shield is Lord God" (Psalms 84:12). And just as the moon darkens and lightens, so too is Israel; just as we say in the blessing "and to the moon They said, 'renew yourself!' - a crown of glory to the womb-borne, for they are destined to renew themselves like it." And just as the moon exists even in the days of its diminishment [waning], when it seems dark on Earth -- it however is light on its other face from above, as is known; so too Israel. And for all of these reasons, Israel accepted this commandment with joy.