parshanut torah comment - Why was the first mitzvah given to B'nai Yisra'el the one dealing with sanctifying the New Moon?

In an epic explanation of the first verse in the Torah, Rash"i cites Rav Yitzhak's question, why the Torah did not begin with the mitzvah in Shemot 12:2

This month is for you the head of the months...

which is the first commandment given to B'nai Yisrae'l (i.e. as a communal group / nation.)

Of the many mitzvoth that are in the Torah, why was this one chosen, specifically? Perhaps, a more "fundamental" mitzvah such as the 1st of the 10 commandments (belief in the uniqueness of G-d) or observance of Shabbat, or anything else, might have been chosen?

I'm surmising that a calendar is, in a way, an identification of one's culture and, maybe, the concept of "time management" is important to unify the people (otherwise, everyone could be celebrating holidays at a different time. Although, in a sense, that's still done (2 days Yom Tov because of "doubt".)) But Shabbat and numerous other mitzvot are certainly important in terms of "unity" and nation identification.