The first Mitzvah that Moshe taught us was to sanctify the new moon and to follow a lunar calendar that begins with Nissan (Parashas Bo, 12:2). Included in this Mitzvah is the requirement to institute leap years to ensure that Nissan falls in spring, the season of natural renewal, as well as of the renewal of our nation through the Exodus. To appreciate the significance of this Mitzvah to our people at that time, we need first to reflect on the symbolism of the solar calendar that was followed by their Egyptian masters.

The Egyptians’ choice of a solar calendar may be associated with the fact that they worshiped the sun (Abarbanel to Yirmiyah 43:3). The sun rises every day from the same direction it rose the previous day, with no noticeable sign of change. The rest of the natural world likewise continues along its perpetual course, and there is nothing new under the sun (Koheles ch.1). Their Hebrew slaves were even more restricted in this respect, for they lacked the independence to make choices and create changes.

In contrast, the moon changes from day to day, and once a month it experiences a renewal that is displayed around the world. When we were released from the clutches of the Egyptians and granted the Mitzvah to sanctify the moon’s renewal, we were granted independent power to define the sanctity of time, the fabric of reality, by designating the day of the moon’s renewal. This newfound independence would come with its ups and downs, as we rise and fall corresponding to our choices, just as the moon waxes and wanes — but all this is part of the process of growth.

We were commanded to mark Nissan, the beginning of our nation, as the first month, as opposed to Tishrei, the beginning of the world. This meant that we would no longer view ourselves as regular human beings locked with the confines of nature, who began with the beginning of the world in Tishrei, but rather as a class of human beings who can control the universe, who date back to the Exodus of Nissan (see Abarbanel and Rav Hirsch to 12:2). Until then, like the nations, we were under the astrological influence of the constellations. From then on, to the contrary, we control the months, along with the influence of their associated astrological signs (Olelos Ephraim §51). This means that a Jew can merit to be impervious to any astrological influences (see Shabbos 156a and Olelos Ephraim §5).

Not only do we have a Mitzvah to sanctify Rosh Chodesh. Rosh Chodesh sanctifies us. The festivals, which all depend on our designation of Rosh Chodesh, bring sanctity to us and develop our relationship with Hashem, and Rosh Chodesh itself is a miniature festival that affects us similarly. Pesach, Shavuos, and Sukkos correspond to the Patriarchs, and the twelve festivals of Rosh Chodeshcorrespond to the twelve tribes (Abudraham, Rosh Chodesh). When the Jewish men sinned with the Golden Calf, Rosh Chodesh lost much of its festival status, but it is still commemorated through a festive meal (Orach Chaim 419:1). Through the renewal of Rosh Chodesh, we merit atonement. Some, therefore, have a custom to fast on the day before Rosh Chodesh, which is called Yom Kippur Kattan, a miniature Yom Kippur.

On a deeper level of understanding, the moon’s reflection of the sun’s light symbolizes the reflection of Hashem’s light. Thus, Jewish kingship, which reflects Hashem’s will in the world, is compared to a moon. Just a moon reaches fullness after fifteen days and then disappears after another fifteen days, Jewish kingship ascended fifteen generations from Avraham until King Shlomo and then declined until the destruction of the Beis HaMikdash fifteen generations later (Shemos Rabbah 15:26). And just as the moon renews itself without fail, the Jewish people will soon become renewed in full splendor under the leadership of Mashiach, never to wane again. For this reason, when we recite the blessing over the new month, we say, “David, melech Yisrael, chai v’kayam!” (David, king of Israel, lives on!), meaning that the Davidic dynasty lives on despite its apparent disappearance and that it will one day be renewed like the just-witnessed phenomenon of the moon’s renewal. We conclude the ceremony with a brief dance, which resembles a wedding dance, to symbolize the future renewal of our marriage-like relationship with Hashem (Orach Chaim 426:2).

This idea, that the moon’s reflection of the sun symbolizes how we reflect Hashem's will, is related to the aforementioned idea that our ability to designate the moon’s day of renewal symbolizes our ability to define the sanctity of time. For, to the extent that we reflect Hashem’s will, we represent the King of the universe, and this empowers us to control the world according to His will. We will only be able to do so fully when Mashiach comes and the Davidic moon becomes full again.

Since the Jewish women refused to part with their golden earrings for the formation of the Golden Calf, Hashem rewarded them in this world by granting them to observe Rosh Chodesh more than men, and in the next world by renewing them like Rosh Chodesh (Pirkei D’Rabbi Eliezer §44; see Hilchos Chag B’Chag Rosh Chodesh,ch. 5, for halachic details). The moon relates to women in particular, because a wife reflects her husband’s will similar to the way the moon reflects the sun’s light. Accordingly, the renewal of the moon’s light is especially symbolic for women, for their marital relationship experiences a similar renewal through the monthly cycle (Ohr Zarua,Vol. 1, Niddah §360).

Although these days we no longer sanctify the new moon, we can all connect with this Mitzvah by taking stock of our deeds before Rosh Chodesh and planning improvement in the coming month, lauding Hashem for His renewed kindness through the recital of Hallel, reciting the Mussaf prayer that corresponds to the Rosh Chodesh Mussaf offering, and observing this richly symbolic day as a miniature festival. We are celebrating our renewed relationship with Hashem, the opportunity to reflect His will in the new month, and the belief in our upcoming national renewal that is symbolized by this day.