LEAD TIDBIT
Pre-requisite of Nationhood
Yaakov's family went to Mitzrayim as technical B'nei No'ach. That means that they officially were bound to keep the mitzvot included in the Seven Noahide Laws. As the Exodus drew near - as a much, much larger family/nation, they received the commands related to their first Pesach - not exactly the same as Pesach L'Dorot, the Pesach that would be part of the Torah and Mitzvot to be observed by the Jewish People in perpetuity - but an additional set of commands, nonetheless. On their way out of Egypt they received several more mitzvot, and then came the Sinai Experience - Matan Torah, where and when the people received all of the Torah (although it was spelled out to them - us - over the years that followed).

One mitzva stands out and grabs our attention in Parshat Bo, the mitzva that Rashi said would have been the logical starting point of the Torah, had it been only our code of law. That mitzva is Kiddush HaChodesh, the setting up of the Jewish Calendar. It would have been hypothetically possible for G-d to have commanded the people about the Korban Pesach and everything that went with it, and hold off on the Calendar mitzva until Sinai. But He didn't wait. The Torah makes a point that G-d spoke to Moshe and Aharon about this mitzva, when they were still in the Land of Egypt.

This (perhaps) makes Kiddush HaChodesh more than a "regular" mitzva, more even than a fundamental mitzva and principle of Judaism; it makes it a Pre-Requisite of Nationhood.

Of course, for practical reasons, if the Korban Pesach was to be offered on the 14th of Nisan, the people must know what Nissan is. But there is more to it than that.

Many nations existed before Bnei Yisrael became a nation. And many more have come and gone since. They were, are, and will be "merely" nations. we are G-d's partners. He sanctifies time and taught us to do so as well. Part of what makes us a holy nation is our Calendar. It still is. Always will be.