Shabbos HaGadol, the Sabbath before Pesach (Passover) commemorates the tenth of Nissan: “Speak ye unto all the congregation of Israel, saying: In the tenth day of this month they shall take to them every man a lamb, according to their father’s houses, a lamb for a household” (Exodus 12:3, JPS 1917 Tanach). This lamb was to be without blemish (Exodus 12:4). And ye shall keep it unto the fourteenth day of the same month” (Exodus 12:6).
The sages explain that this Passover lamb was tied to the bedposts in the homes of the B’nei Yisrael in Egypt. The lamb was inspected for four days for blemishes. On the afternoon of the fourteenth of Nissan at dusk the lamb was slaughtered; its blood was placed upon the doorposts and lintels as a sign. “The blood shall be to you for a token upon the houses where you are; and when I see the blood, I will pass over you, and there shall no plague be upon you to destroy you, when I smite the land of Egypt” (Leviticus 12:13).
What is the significance of Shabbos HaGadol today? In other words, why do we commemorate this day in particular? The tenth of Nissan was on a Shabbos, preceding the redemption. Therefore, its commemoration is always on the Shabbos that precedes Pesach, irrespective of the actual date on the Hebrew calendar. For example, the tenth of Nissan was on Tuesday, whereas this Shabbos will be the fourteenth of Nissan.
Because the lamb was a deity to the Egyptians, they were none to happy about being told, when they asked their Jewish neighbors about the lambs each family obtained, that the lambs would be slaughtered. Yet, despite their angst, we proceeded, with H’Shems protection on the Great Sabbath. The redemption was put into motion, in its final stage. Those four days that passed served as a countdown to the Exodus. The blood of the lamb protected the Jewish homes from the plague of death; and, procured our redemption through the demonstration of our emunah (faith) towards HShem.