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.
Without miracles, we might come to believe that the laws of physics define reality. Once we witness the inexplicable, we see that it’s not a closed system, that there is a higher reality.
And then we look back at physics and say, “This too is a miracle.”
The miracle of a small flask of oil burning for eight days was this sort of miracle. The combustion of oil and oxygen generated light, and yet the quantity of oil did not diminish.
Then there are those small miracles that occur every day, those acts of synchronicity we call “coincidence,” because in them G‑d prefers to remain incognito, leaving all the laws of nature intact.
Indeed, that is an even greater miracle, that G‑d can achieve whatever He so desires non-invasively, as though He weren’t even there.
These were the sort of miracles the tiny band of Maccabees saw in their battles against the mighty Greek army. They fought bravely, but in their hearts they knew a great miracle happened here.
So too, when we open our eyes and hearts, we ponder those everyday coincidences and we awaken to the realization that there is truly no place void of this wondrous, unlimited G‑d.