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

Question

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.

Answer 1

I found the explanation in the commentary in the Hirsch Chumash Shmos 12:2 translated to English by his grandson Rabbi Levy. I got it many years ago but you should find new editions via google such as Feldheim Publishers

Rav Hirsch goes into a very lengthy explanation of the meaning of this mitzvah and why it is the first mitzvah received as a nation and what it means for the nation. Since it is so long, I will be able to give only a few exerpts that summarize this meaning.

First, Hashem wants to ensure that Bnai Yisrael do not fall prey to the error which caused Par'o to fall.

He began the construction of the inner life of His people by the institution of an אות This regular, periodically recurring sign wa always to draw the looks and the thoughts of the people afresh up to Him. It was to summon them to ever fresh rejuvenation out of the darkness of error and depravity and so to ensure a constant rebirth to truth and purity that would forever protect Israel from Egyptian spiritual and moral insensibility.

This was similar to the covenant of the rainbow after the flood, establishing the meaning.

Rav Hirsch then points out that the Bnai Yisrael knew the astronomical cycles, but the requirement to actually see the new moon for Rosh Chodesh to occur had a deeper meaning. In fact, this requirement in and of itself proves that they already knew when it would occur, especially since many months could not be seen as during the rainy season.

As a matter of fact, the תורה שבעל פה (Rosh Hashana 23, 24, 25) tells us that calculation was at the base of the fixation of the moment of the possibility of the new moon being visible.

It is the subjective taking note that is the significant part of the ceremony and it is to be לכם that the Bnai Yisrael are to establish the calendar and recognize their position in the world as Hashem has commanded.

Just as it, bound by physical laws, rejuvenates itself, so are you, but of your own free will, to create your own rejuvenations.

This is why the laws of Rosh Chodesh are the start of the mitzvot as a community. Unlike the heathen who cannot recognize the freedom that Hashem has granted man, we see that Hashem has set up the universe so that we can progress and renew ourselves.

A further reference points to Rav Soloveitchik's explanation (Gesher 1960) of this mitzvah (Search for Chizuk and Idud on page 27 of Parshas Bo 5777 Torah Tidbits

The basic idea is that an eved cannot have any control of time. As a result, the first mitzvah of bnei Yisrael on becoming free is the control of time. Indeed that is why we have the bracha in musaf of Yom Tov that falls on Shabbos (as an example)

מקדש השבת ישראל והזמנים

Shabbat is determined by Hashem and occurs every seven days. However, the Moadim are determined by the declaration of Bais Din when Rosh Chodesh is announced. Thus, the moadim are mekudash because of the sanctification of Bnei Yisrael.

Why indeed was Kiddush haChodesh chosen to be given first, before all of the other mitzvot? What unique quality is to be found in this mitzva?

We might ask: What does redemption from slavery have to do with the blessing of the new month? Rav J.B. Soloveitchik zt”l (Gesher June '66) suggested that a slave's existence is one devoid of time-awareness and time-consciousness. A slave lacks both of the above since he is not master of his own time. The master owns not only the body of his slave, he possesses and regulates the slave’s every waking moment. AVADIM HAYINU - as slaves in Egypt, our time was not our own. In essence, R' Soloveitchik's comments expand upon the words of the S'forno: HaChodesh Hazeh Lachem - “from this point onwards the months shall be yours to do as you see fit. During the days of bondage, however, they did not belong to you. They existed instead for the purpose of serving others and doing their will. Consequently, this month will become the head of the year, for on this month (Nissan) you (the Jewish People) have begun your free existence."

Answer 2

Rabbi Yonah H. Geller z"l, stated in my hearing that "only a free nation has a calendar;" (since time belongs to HaShem we were chosen and given the mitzvah to sanctify time;) so the short answer is this is the first Mitzvah HaShem commanded to us (Bnai Yisrael) because it is our beginning of The Nation as a free people.

Because we (Yisrael) are referred to as HaShem's firstborn (Shmoth 4.22), we sanctify time in all places.

Freed from slavery, the Jewish people were presented with a sudden treasure of time. As slaves, their time had been taken from them, but now they had a prophet who got it back. What would they do with this segulah?

When sanctifying the new month, the Beth Din declares, “Mekudash, mekudash! Sanctified, sanctified!” Hashem gave the Jewish people the power to sanctify time by what they say and do, not only to give it worth, but to infuse it with holiness. Rosh Chodesh, the first day of the new month, has the status of a minor festival. Tehillim (Psalms) 81.4 reminds us that we can sanctify the moon's renewal of our lives. By living in a way consistent with Torah, we sanctify our time and preserve it for all eternity. The mitzvah of Rosh Chodesh Nissan delivered the gift of time.

The root used in the Torah is Rosh, meaning head or first as in first born, which is related to rashut.

But before the root, we read "HaChodeesh hazeh lacheem" and the implied meaning is that HaShem set the month of Nissan (spring) before Moshe and Ahron as a choice (Choose you this day life...Deuteronomy 30:15-20).

As sabbahillel points out, "In essence, R' Soloveitchik's comments expand upon the words of the S'forno: HaChodesh Hazeh Lachem - “from this point onwards the months shall be yours to do as you see fit."

Here, Moshe, Ahron and the entire Children of Yisrael are given a leadership role (olam hazeh and olam habah - the present status of things being temporal) as demonstrated by their ability to set apart the month of Nissan as the beginning of months. Since we follow the "correct calendar" (lunar/solar), Pesach always fall in the spring on the day in which HaShem liberated us from slavery.

Rashut (with a kamatz) means "authority". A related term reshut (with a sheva) means permission. (Another term, reshet means net-work as in Shmoth [Exodus] 27:4.) Avshalom Kor [in Yofi Shel Ivrit (chapter 31)] "writes that rashut comes from the word rosh ראש - "head". Klein agrees, and writes that the word is "probably a shortened spelling for rashut with an alef - ראשות"."

The very next commandment after "sanctification of the new moon" is to "draw out and slaughter the god of the Egyptians" before their eyes!

Since we have "authority" to sanctify the new moon; as a public act (Shmoth 12.1-2), we don't need permission for a public act. "In the private domain - only the individual has permission to act, whereas in the public domain the entire public can do as they please." http://www.balashon.com/2007/07/rashut-and-reshut.html