The Shabbat before Pesach (Passover) is called “Shabbat Hagadol” (the “Great Shabbat”) for a number of reasons:

1) The primary event commemorated on this Shabbat is a great miracle which occurred on this day, several days before the Exodus. 

The Jewish people were commanded by Moses to take a lamb and tie it to their bedposts on Shabbat, the 10th day of Nissan, five days before they were to leave Egypt. 

When the Egyptians inquired by the Jews why they were buying lambs en masse, they were told that these lambs were intended for the Paschal Offering, which would be sacrificed in preparation of the Plague of the Firstborn. 

For some reason, this information rattled the Egyptian firstborn, who immediately insisted that Pharaoh grant the Jews the liberty they demanded. 

When Pharaoh refused their request, the Egyptian firstborn waged war with Pharaoh’s army, and many Egyptians who were guilty of atrocities against the Jews were killed on that day.


Why We Celebrate Shabbat Hagadol instead of the 10th of Nissan

Why do we commemorate the miracle on the Shabbat before Passover rather than on the tenth of Nissan, the date on which it actually took place? We see that the Torah itself mentions only the date rather than the day of the week.

It is because the miracle is closely connected to Shabbat. The Egyptians were aware that the Children of Israel observed Shabbat and did not busy themselves tending animals on that day, so when the Egyptians saw them taking lambs and binding them to their bedposts on Shabbat, they were surprised and decided to investigate what was happening.

The Children of Israel were in great danger when they were confronted and were saved only by virtue of a miracle. We therefore commemorate this miracle on Shabbat rather than on the tenth of the month of Nissan.

Moreover, had it not been Shabbat, the Children of Israel would not have needed a miracle to save them. 

They would have been able to deceive the Egyptians by diverting their attention or making up some kind of explanation. 

On Shabbat, however, they would not do so, for, as our Sages said, “Even an ignorant man will not tell lies on Shabbat.” Thus, we see that they were endangered because of their observance of Shabbat, and they needed a miracle to save them.

Article taken from www.chabad.org