Why Israel Counts by the Moon and the Nations by the Sun

"This month shall be for you" (Exodus 12:2). You count by months (that is, by moons), but the nations of the world count by days. Said Rabbi Abin the Levite: It is the way of the world that the great one counts by the great, and the small one by the small. Esau, who is the elder, as it is said, "her elder son" (Genesis 27:15), counts by the sun, which is the great one, as it is said, "the greater light" (Genesis 1:16). Jacob, who is called the younger, as it is said, "her younger son" (Genesis 27:15), counts by the small one, by the moon, as it is said, "and the lesser light" (Genesis 1:16). Thus, "this month [shall be for you]."