On the Shabbat before the Exodus--Nissan 10th on that year--the first-born of
Egypt, who occupied the senior positions in the priesthood and government,
fought a bloody battle with Pharaoh's troops, in an effort to secure the release
of the Israelites and prevent the Plague of the Firstborn. This "great miracle" is commemorated each year on the Shabbat before Passover, which is therefore called Shabbat HaGadol, "The Great Shabbat." (This is one of the rare instances in which a commemorative date in the Jewish calendar is set by the day of the week rather than the day of the month.)
On this day, King Hezekiah, the greatest of all the Judeaen kings, fell seriously ill, and was informed by the Prophet Isaiah that he would die, for G-d was displeased with the fact that Hezekiah had never married.
Hezekiah had refused to get married because he had prophetically foreseen that his children would lead the Jewish people to sin. He erred, for it is man's job to heed the commandment of procreating, and the rest is in the hands of G-d.
Hezekiah asked the prophet to pray on his behalf, but he refused, insisting that the Heavenly decree was final. The king asked the prophet to leave, saying that he had a tradition from his ancestors that one should never despair, even if a sharp sword is drawn across one's throat. The king prayed to G-d, and his prayer was accepted. G-d sent Isaiah to tell him that he would recover and that his life would be extended for fifteen years. Hezekiah recovered three days later, on the first day of Passover.
A year following the building of the second Temple in Jerusalem (see Jewish History for the 3rd of Adar) Ezra gathered many of the Jews who had remained in Babylon and began a journey to the land of Israel. Though he certainly wanted to go earlier, his teacher, Baruch ben Neriah was too frail to travel, and Ezra refused to leave him until his passing.
Ezra was the head of the Sanhedrin, who all traveled together with him.
On the 12th of Nissan, Ezra departed from the river of Ahava, the beginning of the long journey to the land of Israel which would last for nearly five months (see Jewish history for the 1st of Av).
The Shabbat before Passover is termed Shabbat HaGadol
("The Great Shabbat") in commemoration of the "great miracle" that happened in Egypt on this day, heralding the Exodus from Egypt five days later (see "Today in Jewish Hstory"). Shabbat HaGadol customs include reading a portion of the Haggadah (from "Avadim hayinu..." to "...al kol avonotainu"), which tells the story of the Exodus; it is also customary that the rabbi of the community delivers a lecture in which he elaborates on the laws of Passover and their significance, in preparation for the festival.