on this day it was demonstrated that the Egyptians were powerless against the Jews. They must have been mightily peeved by the fact that the Jews were planning to slaughter lambs, an Egyptian deity -- but were incapable of doing anything to hamper their plans.
Some suggest that this Shabbat earned the title "Gadol," because it is the day when the rabbis traditionally deliver extensive lectures about the laws of Passover, and pontificate about the lessons to be learned from the holiday.
The Haftorah read in many communities on this Shabbat speaks of the coming of Moshiach, referring to the day of his arrival as the "yom Hashem hagadol v'hanora" -- the "great" and awesome day of the L-rd
