The Shabbos that precedes the festival of Pesach is known as Shabbas HaGadol, the “Great Shabbos.” The day commemorates the miracle that transpired with the Jewish people on the tenth of Nissan, which that year fell on the Shabbos just prior to the Exodus.

The Rabbis have asked1 why the commemoration of this event was assigned to the day of Shabbos, rather than to the tenth of the month. Why, they ask, is Shabbas HaGadol different from all other festivals, which are celebrated on the anniversary of the day of the month, not on the anniversary of the day of the week?

The relationship of Shabbas HaGadol to the day of the week will be understood if we consider the reason that all other festivals are celebrated according to the day of the month.

The difference between the days of the week and the days of the month is that the days of the week are bound up with the Days of Creation and the world itself — “For in six days, G‑d made the heavens and the earth, and on the seventh day He ceased from work and rested.”2

The concept of a “month,” however, is a later addition. As our Sages state:3 “When G‑d chose His world, He [then] established within it new months.” Thus, months are not bound up with creation and nature itself, but with G‑d’s choosing to insert months into the equation. As such, “months” denote an additional quality that G‑d imbued “within His world.”

The difference between days of the week and days of the month is also connected to the very nature of weeks and months: weeks, composed as they are of a seven-time cycle of day and night, are related to the sun, while the days of the Jewish month are related to the cycle of the moon.4

The illumination of the sun is constant, like the unchanging quality of nature, while moonlight, which waxes and wanes and is always in a state of change, is symbolic of the fluctuations between natural and miraculous events. Thus, the cycles of the moon are symbolic of an addition to creation — the miracles that transcend nature.

Since all Jewish holidays and festivals celebrate revelations of G‑dliness that transcend nature5 (i.e., and therefore are related to the nature of the moon),it follows that they are all celebrated on the day of the month on which they first occurred.

The reason the miracle of Shabbas HaGadol is not celebrated in accordance with the day of the month but in accordance with the day of the week will be understood accordingly.

The Alter Rebbe explains the miracle of Shabbas HaGadol in the following manner:6

“The Shabbos before Pesach is called Shabbas HaGadol since a great miracle occurred on that day. For ... when the Jews took the lambs for their Paschal offerings on that Shabbos, the Egyptian firstborn assembled before them and inquired why they were doing so. The Jews responded: ‘This is our Paschal offering, for G‑d shall slay the Egyptian firstborn.’

“[Thereupon] the firstborn went to their fathers and to Pharaoh and demanded that they liberate the Jews. When they refused to do so, the firstborn declared war against the rest of the Egyptians and killed many of them. This is the meaning of the verse, ‘…Who struck Egypt through its firstborn....’7 It was instituted that this miracle be remembered in future generations on this Shabbos, which is therefore known as Shabbas HaGadol.

At first glance, the entire incident seems to be a natural event: After having experienced the first nine plagues, it is no wonder that the firstborn believed they were about to be smitten. Thus, when their elders refused to allow the Jews to leave, it was quite natural that they rose up and killed many of them.

Thus, the miracle of Shabbas HaGadol lay not in overpowering nature with a supernatural revelation from Above, merely that nature itself underwent a change: The Egyptian firstborn — until then the most powerful of the oppressors8 — did all they could to have the Jews expelled from Egypt.

The miracle of Shabbas HaGadol is therefore linked to the days of the week — the course of nature — for it involved a change within nature itself. That is why this miracle is always celebrated on Shabbos rather than on the tenth of Nissan, for it more closely relates to days and nature, than to months and the supernatural.

Based on Likkutei Sichos, Vol. XXVII, pp. 44-46.