“This month is for you the ‘head’ of months, the first of the months of the year it shall be for you” (Shemot 12:2). The Mechilta (Bo 1) comments on this: Moshe had trouble telling when the new month was considered to have come … until Hashem showed him the moon as it was renewed and said to him: “See the moon when it is like this and sanctify it.” The nations of the world count from Tishrei; Israel counts from Nisan. We have a tradition that Nisan is the month of liberation: “In Nisan they were liberated; in Nisan, they are destined to be liberated” (Rosh Hashana 11a).
