The Tur on Orach Haim explains the reason why we call this coming Shabbat ‘Shabbat Hagadol’, ‘The Great Shabbat, as follows:
“The Shabbat before Pesach is called ‘The Great Shabbat’. The reason is that a great miracle occurred on that day, for on that year, the lamb for the Pesach offering was set aside on the tenth of the month of Nissan. As it is written: ‘On the tenth of this month, and they shall take for them a lamb for each family, a lamb for each household.’ Pesach, when Israel went out of Egypt was on a Thursday, as is written in Seder Olam. Thus, the tenth of the month was on Shabbat, and each head of household took a lamb to be set aside for his Pesach offering and tied it to the foot of his bed. The Egyptians asked them: ‘What are you doing?’ And they answered, ‘To slaughter it for Pesach, as G-d has commanded us!’ And their teeth became blunt because the Jews were slaughtering their deity, but they were not permitted to say a thing. In commemoration of that miracle, we call it ‘The Great Shabbat’.”
In other words, a number of days before the exodus from Egypt, while our ancestors were still in the ‘House of Bondage’, they already displayed signs of liberty by following G-d’s word without receiving the approval of their Egyptian masters. Designating a lamb for ritual slaughter, despite the fact that the Egyptians considered the lamb a deity, was diametrically opposed to the Egyptian lifestyle and faith-system. This was the great miracle. The Children of Israel, slaves in Egypt, conducted themselves as a liberated people by preparing the lamb for slaughter; obeying G-d’s word, and not the orders of their Egyptian slave masters.
In our day and age, we must remember the liberated conduct of our ancestors, which was the merit they needed to emerge from slavery to liberty. For without preparing the lamb as G-d commanded, our ancestors would not have been able to be redeemed from Egypt. We see, therefore, that the first condition for redemption is for those being redeemed to conduct themselves as free people.
May we conduct ourselves with true liberty and connect to our Jewish identity with joy on this Pesach holiday.