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.
How to unmask a blessing in disguise:
Stare it in the face and say, “I know you are not just a lousy day or bad luck. I know you are a good friend—even if for the life of me I cannot determine how. I know there is only one Source of All Things, and nothing can convince me that evil descends from Above. Evil descends from the constraints of my perception. You are no more than a blessing in disguise.”
This blessing, if truly a great one, will not surrender its cover easily. You will need a composure that demonstrates you meant every word you said. You will need to hold your ground like a mountain against the sea. You will need to surprise yourself with your own resolve.
And then you can turn over a world. A world that once distorted every blessing that squeezed through its gates will now open those gates wide. And the blessings that have already entered will sigh a breath of relief as one by one they discard their scary costumes.