Kozhiglover on why this shabbos is called shabbos ha'gadol

My son quotes a letter of the L Rebbe in which he writes that it's not by accident that Pesach comes in chodesh ha'aviv.  During the long winter months it looks like nothing is alive, nothing can grow, but then suddenly the weather changes, the trees are blossoming and we can say birkat ha'ilanot, and the flowers and grass start sprouting again.  These winter months were a necessary preparatory step to allow things to bloom again; just because nothing was visible on the surface does not mean nothing was taking place.  So too in life, there are periods when we feel like we are stagnating and in a funk and not progressing, but these are just passing winters, and a new spring will eventually arrive.  This is the lesson of galus Mitzrayim, where it seemed we had sunk to irredeemable levels, but suddenly geulah happened and we blossomed forth as a nation. 

I would add the words of the Midrash Rabbah (Braishis 10:6):

 אָמַר רַבִּי סִימוֹן אֵין לְךָ כָּל עֵשֶׂב וְעֵשֶׂב, שֶׁאֵין לוֹ מַזָּל בָּרָקִיעַ שֶׁמַּכֶּה אוֹתוֹ, וְאוֹמֵר לוֹ גְּדַל

It is Shabbos haGadol.  Throughout the year we may be unaware of that malach standing above and may not hear the whisper commanding  גְּדַל.  This Shabbos, this time of year, all of us hear it's call.

But it is not just a whisper.  מַּכֶּה אוֹתוֹ**, וְאוֹמֵר לוֹ גְּדַל**.  Growth is hard and growth can be painful.  That is true for us as individuals and true for us as a nation.  But grow we must.

Why is this shabbos called Shabbos haGadol?

In Parshas Braishis we read (1:16) that Hashem made אֶת⁠־שְׁנֵ֥י הַמְּאֹרֹ֖ת הַגְּדֹלִ֑ים, but then the pasuk continues and tells us  that there is    אֶת־הַמָּא֤וֹר הַגָּדֹל֙ לְמֶמְשֶׁ֣לֶת הַיּ֔וֹם וְאֶת־הַמָּא֤וֹר הַקָּטֹן֙ לְמֶמְשֶׁ֣לֶת הַלַּ֔יְלָה.  Rashi comments:

  שוים נבראו, ונתמעטה הלבנה על ידי שקיטרגה ואמרה: אי איפשר לשני מלכים שישתמשו בכתר אחד.  

The Kozhiglover explains that the difference between the sun and the moon is not merely a matter of size, but rather lies in the fact that the sun gives light, but the moon merely reflects light.  The gemara in Bava Metziya (12b) tells us  גדול וסמוך על שלחן אביו זהו קטן קטן ואינו סמוך על שלחן אביו זהו גדול  A gadol gives; a katan receives.  Similarly the gemara in Nedarim (24a) writes that a neder made to force someone to reciprocate a gift is taken seriously because the noder might be thinking  לאו מלכא אנא דמהנינא לך ואת לא מהנית לי .  I don't want to be like a melech, as a melech gives without taking in return.  The moon argued that there could not be two melachim, two gedolim, two bodies that give off light independent of each other.  As a result, it became a katan.  It no longer is able to give off light, only to receive and reflect it.

The masechta in shas dedicated to the laws of chol ha'moed is called Moed Katan.  Chol haMoed receives its kedusha from the days of Y"T that precede and come after it.  These days are the sibah for its issurim; chol ha'moed merely reflects their light.  The Kozhiglover explains that the machlokes whether to put in tefillin on chol ha'moed revolves around this point: do we look at the fact that it has no independent kedusha apart from that which comes from the days of Y"T that surround it and therefore treat it like chol, or do we say that sof sof the fact that it reflects that light of Y"T is enough to push of tefillin. 

This is also the difference between Eretz Yisrael and chutz la'aretz.  Ramban famously writes in P Acharei Mos that mitzvos should in theory only apply in Eretz Yisrael, but in chu"l we do them in order to keep in practice.  Eretz Yisrael is the source of light; chu"l merely reflects what Hashem channels through Eretz Yisrael.

Pesach is the first of the regalim and is called a day of shabbos (the omer is brought "mi'macharas ha'shabbos"), but there is a source of light even greater than itself.  Shabbos is תחילה למקראי קודשׁ, it is the primal source, the source from which springs the kedusha of all the other Moadim of the year, the first of which is Chag haPesach.  This is why our shabbos is called Shabbos haGadol.  It is the well from which Pesach and the other Moadim all draw, the source of the kedusha that we will IY"H receive and grow from in the upcoming week.