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.
For a mitzvah is a candle and Torah is light. (Proverbs 6:23)
Every mitzvah shines its particular light into our world. And there will come a time when you will see that light with your eyes.
Except the candles that are lit for Shabbat before sunset. They shine a light you can see right now.
It may seem an ordinary light, just another flame. But there is nothing ordinary about it.
You have ignited the darkness of our world and extracted its secret:
That it too is light.