The name of the current Hebrew month, Nissan, comes from the Hebrew word "nes", meaning "miracle", because of all the miracles the Almighty did with the Jewish people to redeem them from the slavery in Egypt. Nissan is known as "the Month of Redemption", because its main event is Pesach.

The Rebbe explains that redemption is especially emphasized this Shabbat, called "Shabbat Hagadol" - literally "the Big Shabbat" - because it corresponds to the Shabbat before the Exodus, when G‑d caused a great miracle to happen. As commanded, the Israelites prepared the Pascal lamb on the 10th of Nissan, which fell on a Shabbat, as it does this year. When questioned by the Egyptians, the Jews explained that these lambs would be sacrificed on the 14th of Nissan (the eve of Passover), and that night G‑d would slay all the firstborn of Egypt. The firstborn Egyptians then went to their parents and Pharaoh, begging that Israel be released. When this request was denied, the firstborn rose in armed revolt. The result was a big miracle, Egyptians killing Egyptians, setting the stage for the redemption. Still, what is the big deal? G‑d did many miracles for the Jewish people! Why call this a big miracle? The answer is that in all the other miracles, our enemies were killed by G‑d, but in this case, it was our enemies who killed our enemies.

Note the order of events leading up to the seder:

We burn the chometz…spiritually destroying any remaining barriers between ourselves and the Divine….

The search for chometz is in the evening, 24 hours before the seder night, immediately after the evening prayers. It is not only a physical search, but a spiritual one as well - we must check ourselves for pride - spiritual leaven, the great separator between man and G‑d. (If you have not yet done so, that evening is the last easily available time to sell your chometz to your local rabbi.) The following morning we burn the chometz we found, spiritually destroying any remaining barriers between ourselves and the Divine. We stop eating chometz by midmorning (check with your local rabbi or Jewish newspaper for the correct times), and sometime in the afternoon, we read about the bringing of the Pascal lamb. We say the evening holiday prayers with much joy and add the Hallel prayers to the regular service. We start the seder as early as possible to allow our children the maximum chance to participate.