The Shabbat preceding Passover is known as "Shabbat Hagadol", The Great Shabbat.
Why?
When the Israelites were still in Egypt they were given a command, 5 days before the Exodus occured. That command was to take a lamb and tie it to their bedposts. This made the Egyptians ask the Israelites why they did so, to which the Hebrews responded that this was in preparation for the impending exodus from Egypt. The fact they got away with this blatant display of defiance without being harmed was a great miracle, which we commemorate to this day every Shabbat prior to Passover.
The Haftorah, (the portion of the Prophets that is read following the Torah reading) is from the book of Malachi describing the coming of Moshiach, "Yom Hashem, hagadol v'hanora" "The great and awesome day of the Lord" which extends its greatness to this Shabbat.
Additionally communities around the world gather on the Shabbat before Passover to hear lectures on the laws of the festival, and when given during the service it lengthens the time in synagogue by a great amount!
Wishing you a blessed Shabbat Hagadol!
