The Shabbat before Pesach is called "Shabbat Hagadol," or "the Great Shabbat," a term that is generally understood as a reference to the miracle that occurred in Egypt on the Shabbat before Benei Yisrael's departure from Egypt. It was on that Shabbat, which fell on the tenth of Nissan, that Benei Yisrael designated sheep for the Korban Pesach (paschal offering) and tied them to their bedposts. The Egyptians inquired as to the purpose behind this designation of sheep, which the Egyptians worshipped as a pagan deity, and Benei Yisrael explained that they prepared the sheep for a sacrificial offering to God. Despite this grave insult to their deity, the Egyptians were powerless to oppose Benei Yisrael. They were miraculously struck by a disease that required them to regularly visit the restroom, thus impairing their ability to cause any harm to Benei Yisrael.
In commemoration of this great miracle that occurred on the Shabbat before Pesach on the year when Benei Yisrael left Egypt, we observe this Shabbat as a special occasion and refer to it as "Shabbat Hagadol."
Some have raised the question as to why we commemorate this miracle specifically on the Shabbat before Pesach, rather than on the calendar date when this miracle occurred – the tenth of Nissan. Why don't we observe a commemoration on this date regardless of the day of week on which it falls?
One answer suggests that it was specifically due to Benei Yisrael's observance of Shabbat that the greatness of this miracle was felt. When they told the Egyptians on that day of their plans to slaughter the sheep as a sacrifice, the Egyptians believed them despite the fact that they did not slaughter the sheep that day, because they understood that Benei Yisrael would not kill animals on Shabbat. On the subsequent days, however, when the Egyptians saw that Benei Yisrael were not yet slaughtering the sheep, they began to suspect that they were bluffing all along. It was thus specifically on Shabbat when the Egyptians sought to foil Benei Yisrael's plans but were miraculously prevented from doing so, and for this reason we commemorate this miracle specifically on the Shabbat before Pesach.
Others explain that the tenth of Nissan marks yet another great miracle in Jewish history – the splitting of the Jordan River when Benei Yisrael entered the Land of Israel, as recorded in the Book of Yehoshua (chapter 3). In order to make it clear that we commemorate the miracle in Egypt, and not the splitting of the Jordan, we observe our commemoration on the Shabbat before Pesach, rather than on the calendar date of the tenth of Nissan.
The Chid"a (Rabbi Chayim Yosef David Azulai, 1724-1806) writes that on this Shabbat people should extend to one another the greeting, "Shabbat Hagadol Shalom" and then respond, "Shabbat Hagadol Shalom U'mevorach."
There is a widespread custom for the Grand Rabbi of the congregation to deliver on this Shabbat a special Derasha (lecture) devoted to the laws of Pesach and discussions of the Haggada in preparation for the holiday. This is another reason for calling this Shabbat "Shabbat Hagadol," which perhaps means, "the Shabbat of the great person," referring to the Grand Rabbi. Additionally, the Derasha delivered on Shabbat Hagadol is typically lengthier than the Rabbi's usual lecture. (The late Chief Rabbi of the Sephardic Community in Brooklyn, Chacham Yaakov Kassin A”H, would deliver his Derasha on Shabbat Hagadol in Congregation Shaare Zion for several hours before Mincha.) The term "Shabbat Hagadol" may thus refer to the "great," or long, lecture that the Rabbi delivers on this Shabbat.
Some Ashkenazim have the practice of reciting the Maggid section of the Haggada on Shabbat Hagadol, in order to familiarize themselves with the Haggada in preparation for the Seder. The Gaon of Vilna (Rabbi Eliyahu of Vilna, 1720-1797) opposed this practice, in light of the emphasis made in the Haggada itself that the obligation to tell the story of the Exodus applies only on the night of Pesach ("Lo Amarti Ela Be'sha'a She'yeish Matza U'marror Munachim Lefanecha"). In any event, even for those of us who do not actually recite the Haggada on Shabbat Hagadol, this Shabbat is an appropriate time to begin reviewing the Haggada and prepare material for the Seder.
