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.)
For more on the war of the Firstborn, see here.
Miriam, the sister of Moses, passed away at the age of 126 on the 10th of Nissan of the year 2487 from creation (1274 BCE) -- 39 years after the Exodus and exactly one year before the Children of Israel entered the Holy Land. It is in deference to her passing that the "Great Shabbat" is commemorated on the Shabbat before Passover rather than the calendar date of the miracle's occurence, Nissan 10.
Link: About Miriam.
Three days after the two spies dispatched by Joshua scouted the city of Jericho (see entry for "Nissan 7" above), the children of Israel were ready to enter the land promised by G-d to their ancestors as their eternal heritage. As they approached the Jordan with the Holy Ark carried by the Kohanim (priests) in their lead, the river parted for them, as the waters of the Red Sea had split when their fathers and mothers marched out of Egypt 40 years earlier. (Joshua 4)
In today's "Nasi" reading (see "Nasi of the Day" in Nissan 1), we read of the gift bought by the nasi of the tribe of Dan, Achiezer ben Amishadai, for the inauguration of the Mishkan.
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.
When the Mighty Waters cover your head, suffocating the soul and the flame that burnt inside . . .
When raging torrents of confusion drag you away in their current, ripping you from your hold on Life . . .
Look deeper. Beyond the soul.
For the soul itself, as well as the flame it holds, are rooted in a serene G‑dly World of Emanation, a world of quietness and sublime harmony.
But the turbulence of this world is rooted even beyond that, stemming from a World of Confusion, of light unbounded and untamed, before the orderly emanation of defined being, “and the world was confused and void, with darkness over the face of the deep.”
So you must dig deeper than those roots, to find the coals from which the flame arose and the flint rock from which the spark was struck. Deeper, until you reach the primordial essence of the soul, beyond Emanation, beyond Light—even beyond the unbounded light of pre-creation. Where there is nothing but the seminal thought which inspired all that is and was and will come to be.
And what was that thought? It was the thought of you here and now, in your struggle with this world, and the delicious taste of your victory.
And, since in that thought there is no past and future, there, in that thought, you have already won.
Now you must make it happen.