This Shabbat is known as Shabbat Hagadol. It is also known as שבת הנס הגדול. The great miracle referred to the taking of the Paschal lamb on the tenth of Nissan, which fell on Shabbat, and the Egyptians did not protest. The lamb was worshipped as a god in Egypt and it was a big surprise that they accepted that these same lambs would be slaughtered as the קרבן פסח.
Another reason it is called שבת הגדול, is because of the words of the Haftarah from the Book of Malachi. The prophet refers to the time when הנה היום הגדול בא, “Behold a great day is coming.” This is referring to the great day of Mashiach that will be preceded by the coming of אליהו הנביא.
This Shabbat is also one where it is customary to hear words of inspiration from the leading rabbi of the community. This is known as the Shabbat Hagadol Drasha.
It is also customary to read parts of the Haggadah in the afternoon between עבדים היינו and after דיינו.
Shabbat Hagadol is a very important Shabbat, indeed. Shabbat Shalom