Ma nishtana Pesach, how different Pesach is, that it has a Parshas HaChodesh preceding it, with the enumeration of the many mitzvos associated with it - there is no special reading of the Torah with the laws of Rosh HaShana, Yom Kippur or Sukkos before those yomim toivm. Parshas HaChodesh gets its name from one passuk (Shemos 12:2) that deals with the mitzvah of Rosh Chodesh and the unique Lunar/Solar calendar that the Jewish nation follow. The remaining eighteen pesukim, however, deal with the laws of Pesach, so why do we refer to this special reading as "Parshas HaChodesh" instead of "Parshas HaPesach"?
I believe that a very insightful Medrash (Shemos Rabbah 15:24) sheds light and clarity on this matter. The Talmud (Sanhedrin 42a) teaches that upon seeing the new moon each month one is to recite a blessing, but the Talmud does not provide us with the text of the bracha. The Medrash posits three possibilities: the first is the text that we follow, reciting a bracha that concludes, "Mechadash Chadoshim - He who renews the months." The second opinion is that of "Mekadash Chadoshim - He who sanctifies months." The third view is "Mekadash Yisroel - He who sanctifies Israel." The Medrash continues and says that we shouldn't be amazed or startled at this last opinion, for indeed if Hashem did not sanctify Israel they in turn could not sanctify the new moon. Thus, the foundation of the first mitzvah given to the Jewish people in Egypt is the special gift and privilege extended to Am Yisrael to sanctify.
There are, our Rabbis note, three different forms of kedusha (holiness): there is the kedusha of zman (time), makom (location), and that of guf - an individual and/or an object. I believe the appellation given to this special reading does not necessarily herald an enumeration of upcoming mitzvos, but rather the opportunities for upcoming sanctifications. In the ensuing eighteen pesukim we encounter all different types of kedusha. We are charged (12:16) that the first and last day are to be mikra kodesh, holy gatherings for proclaiming His holiness, a personification of kedushas ha-zman, sanctifying time. The second kedusha we find is that of kedushas haguf. At first glance it is most strange that the Torah has to charge us (12:17) "ushmartem es ha-matzos - you shall guard the matzos." This guarding must mean something additional to preventing the matzos from becoming chometz since the Torah already warns us (12:15) not to eat chometz. Therefore our Rabbis understand this to mean that we are not simply to bake matza, but we are also to inject into this unleavened bread a lishma - a focus and concentration that charges this bread with an elevated status, as it is now an object of mitzvah. Just as with the writing of a sefer Torah, it is the mindset and focus of the scribe thinking and articulating that his efforts and energies are directed towards the fulfillment of the mitzvah, similarly regarding matzah man endows the matzah with an elevated status, akin to kedushas haguf. Finally, the placing of the blood of the korban Pesach (12:7) on the two mezuzos (doorposts) and lentil was endowing that home with kedushas ha-makom, elevating the home to the status of the mizbeach (altar) which received the blood in place of an altar.
In light of the above, one cannot question why we don't have similar special Torah readings prior to the other yomim tovim. In Parshas HaChodesh we are highlighting not only the first mitzvah given to the Jewish people, namely our unique calendar, but we are also noting that the former slaves are now likened to a klei shares (a holy vessel) that sanctifies all that is placed therein.
The Sefer HaChinuch notes, regarding several mitzvos that focus on the remembrance of the Exodus, that through the events of yetzias Mitzrayim we did not only go from slavery to freedom, but we even went from slavery to aristocracy. Parshas HaChodesh reminds us that our geula (freedom) begins when man is a mekadeish, i.e. when the individual and community endowed with holiness and charged to be G-d like do so by sanctifying all else. Freedom does not mean to do what one pleases within the law (including, for example, doing nothing), rather it means to actualize one's potential of being created in the image of G-d.
Parshas HaChodesh is not only a check list of mitzvos to do and abstain from regarding the forthcoming yom tov. Rather it charges each of us to generate more kedusha in our personal and communal lives. We are not only to gather and remove from our homes ten small wrapped pieces of chometz, but also remove those factors and gadgets that introduce a non-sanctified environment into the home. We don't put blood on our doorposts and lentils, but our dining tables, in lieu of the mizbeach, transform our homes. Are our tables set with divrei Torah or with frivolous conversation? Most importantly, the special reading - HaChodesh - is a charge to sanctify more of one's time by sharing one's Torah and kindnesses with others. If we strive to attain these lofty goals, we can attain the appellation of King David regarding man, "you have made him but slightly less than the angels, and crowned him with soul and splendor" (Tehilim 8:6 .)