In the Torah portion Bo we read that, "G‑d said to Moshe and Aharon in Egypt: 'This month shall be the head month to you; it shall be the first month of the year.'"
We learn from here that it is a mitzvah to "sanctify months, set leap years, and establish the festivals of the year according to the determined sanctification."
Our Sages note that the entire Torah might have begun with this commandment, "for it is the first Mitzvah that the Jewish people were commanded."
The very fact that of all 613 commandments the Torah chose to begin with this one indicates that this mitzvah contains an element fundamental to all the rest.
What is so special about this commandment?
The primary function of the mitzvot is to enable man to permeate the world with goodness and holiness. Thus all Mitzvot involve the transformation of physical objects into Mitzvah-objects, entities of holiness.
This, too, is the overall theme of the commandment to sanctify the new month:
The court sanctifies a certain day and declares it to be Rosh Chodesh, the beginning of the month - not an ordinary working day, and one which establishes when the holidays shall be celebrated.
In addition to the above, this commandment is inherently first in theme and content: Although the world is a composite of both space and time, and time is bound up with space, nevertheless, time precedes space.
For all of Creation, including space, implies an aspect of change - present conditions are compared to the past, i.e., to conditions prior to creation.
Thus, before anything was created, including space, there already existed an entity subject to change - time. Therefore the starting point of all creation is time.
This is true in terms of man's experience as well.
First comes the actual day, and only then can man make an impact on that day by transforming physical objects.
Sanctification of the new month is thus the first commandment, for sanctity is first imbedded in time - the beginning of existence - and only then comes man's interaction with physical objects - the aspect of space.
There is yet another all-encompassing aspect to this Mitzvah:
All of creation was brought about in order to be sanctified through the Jewish people's performance of Torah and Mitzvot.
This is a theme that affects all of creation at all times and in all places.
A Jew's service consists of actualizing and revealing the ultimate purpose within all things. When a Jew performs a Mitzvah with a particular object, he thereby fulfills the object's reason for being, and the object becomes a Mitzvah-object.
For example, when a Jew transforms an animal's hide into parchment for a Sefer Torah, Tefillin, or Mezuzot, that animal's hide attains the purpose for which it was created - the hide has now become imbued with holiness.
Since time, too, is created, it is readily understandable that it is meant to fulfill the same purpose as the rest of creation.
Herein lies the additional significance of this most important command:
Through the Jewish people's sanctification of months - Rosh Chodesh and festivals - they reveal that the true purpose of time is to be sanctified.
For in reality the sanctification of any one month affects not only the establishment of Rosh Chodesh and the festivals in that month, but alters the entire time continuum, so that all of time becomes permeated with the realization that it is to be filled with goodness, holiness, and Mitzvot.
Adapted from the works of the Lubavitcher Rebbe, Rabbi Menachem M. Schneerson, of righteous memory. (Likkutei Sichos Vol. XXVI, pp. 59-65.)