The Shulhan Aruch writes that the Shabbat before Pesach is called by a special name – "Shabbat Ha’gadol." The reason for this name is because this Shabbat commemorates the miracle that occurred for Beneh Yisrael on the Shabbat before they left Egypt. G-d commanded them to prepare a sheep for the Pesach sacrifice four days before the sacrifice was to be slaughtered – meaning, four days before the 14th of Nissan, the afternoon before the Exodus. Beneh Yisrael left Egypt on Thursday morning, which means that the Pesach sacrifice was offered on Wednesday, and thus they needed to prepare it four days earlier, on Shabbat, the 10th of Nissan. The Egyptians, who worshipped cattle, asked Beneh Yisrael what they were doing with the sheep, and Beneh Yisrael explained that they were preparing the animals to be sacrificed to G-d. Although they spoke openly about sacrificing the animal which the Egyptians worshipped, the Egyptians were powerless to do anything, either because of some kind of illness, or out of fear.
This was a remarkable miracle, and since it occurred on the Shabbat before Yesiat Misrayim, we commemorate it on the Shabbat before Pesach, calling that Shabbat "Shabbat Ha’gadol" – "the great Shabbat."
Additionally, the Aruch Ha’shulhan (Rav Yechiel Michel Epstein of Nevarduk, 1829-1908) writes that on this day, the firstborn Egyptians, who had heard Moshe’s warning of the impending plague, took up arms against the other Egyptians who endangered their lives by continuing to refuse to allow Beneh Yisrael to leave. This is the meaning of the verse in Tehillim, "Le’makeh Misrayim Bi’bchorehem" – "To He who smote Egypt with its firstborn," meaning, G-d struck the Egyptians by instigating the nation’s firstborn to wage a fierce battle against them. This, too, is celebrated on Shabbat Ha’gadol.
The question, however, arises as to why the miracles of that Shabbat are celebrated specifically on the Shabbat before Pesach, and not on the calendar date of those events – the 10th of Nissan. Whenever we observe a special day to celebrate a miracle, we do so on the calendar date on which the miracle occurred. Why are the miracles of the 10th of Nissan celebrated not on that date, but rather on the Shabbat before Pesach? While it is true that the 10th of Nissan that year fell on Shabbat, why should we not celebrate the calendar date, as we do whenever we celebrate miraculous events?
One answer is that the 10th of Nissan is the date when the prophetess Miriam, Moshe Rabbenu’s sister, passed away, and it would thus be inappropriate to make this day a day of celebration. Another answer is that it was on the 10th of Nissan when the Jordan River split and Beneh Yisrael crossed into the Land of Israel. If this date were made into a special day of celebration, people would not know whether it celebrates the miracles of the 10th of Nissan in Egypt before the Exodus, or the miracle of the splitting of the Jordan River. Therefore, it was decided to celebrate on the Shabbat before Pesach, instead of the 10th of Nissan.
A much different answer is given by the Aruch Ha’shulhan, who noted that the observances of Shabbat and Pesach are strongly linked to one another, as they express the two most fundamental tenets of Jewish faith – creation and providence. Shabbat commemorates the world’s creation in six days, and thus expresses the belief that the world was created by a single Divine Being, and did not come into existence on its own. Pesach, the celebration of the miracles of Yesiat Misrayim, expresses the belief in Hashagah (providence), the notion that G-d not only created the world, but continues to govern every aspect of the world. He knew exactly where the Egyptian firstborn were, who should be killed and who should be spared, showing us that He oversees everything that happens in the universe. Together, then, Shabbat and Pesach teach us the most basic principles of Judaism – that there is a Creator, and that the Creator is intimately involved in all aspects of our lives and all aspects of the world at every moment. For this reason, the Aruch Ha’shulhan suggests, we celebrate the miracles of the 10th of Nissan specifically on Shabbat – in order to underscore the integral connection between Shabbat and Pesach, between the belief in creation and the belief in providence. Both beliefs are equally crucial tents of the Jewish faith, and cannot be separated from one another, and this is why specifically Shabbat was singled out as the time to celebrate the miracles that preceded Yesiat Misrayim.
Incidentally, it should be noted that after Yesiat Misrayim, G-d did not wait until Matan Torah at Mount Sinai to present the command of Shabbat. Already when Beneh Yisrael encamped in Marah, after the splitting of the sea, the people were told about Shabbat observance. The fundamental belief represented by Shabbat is integrally linked to the fundamental belief expressed by the Exodus, and so immediately after the miracles of the Exodus, G-d commanded the people to observe Shabbat.
Although there are no actual Halachot relevant to Shabbat Ha’gadol, the Hida (Rav Haim Yosef David Azulai, 1724-1806) writes that it is proper on this Shabbat to wish each other "Shabbat Ha’gadol Shalom," instead of the usual "Shabbat Shalom." Since the Shulhan Aruch mentioned that this Shabbat is called "Shabbat Ha’gadol," this should be the "title" given to this Shabbat when we greet one another. Additionally, it is customary for the Rabbi in every community to deliver a special lecture on Shabbat Ha’gadol to prepare the congregants for the holiday. The lecture should combine both practical Halachot relevant to the observance of Pesach, as well as words of Mussar (religious admonition) and inspiration to prepare the people mentally and emotionally for the great Yom Tov of Pesach.
