TZAV - Shabbos Hagadol

This week'sTorah portion is called Tzav. Tzav means “Command.” It expresses a command from G‑d about the donation of offerings in the Sanctuary, relating to the general concept of giving charity. But Tzav also means: “Connect.” It expresses the idea that G‑d’s laws establish a connection between the individual and G‑d.
The very fact that G‑d has issued a command to the person imparts a sense of significance to that person’s life. He or she is now bonded with G-d by a Divine instruction. The Lubavitcher Rebbe points out that this connection is there even if the person does not fulfill the instruction. As the Sages put it, “even though he sinned, he is a Jew.” The fact that the 613 commands in the Torah are addressed to the individual gives that person a significant role and purpose. And of course, this role is properly fulfilled by observance of the commands. Yet the person who does not yet observe them has not lost his role in the system.
When it comes to a command such as charity, in which one has to give something away, we all need encouragement. The Sages tell us that this is the force of the word “Tzav” : to give us encouragement through the generations. The encouragement is the knowledge that through this command of G-d we are truly connected with Him.

This Shabbat, is the Shabbat before  Pesach it's called Shabbat haGadol, the Great Shabbat.

When the Jews were in Egypt, they were commanded on that day to take a lamb and tie it to the bedpost. Which they were later to bring as a Pesach sacrifice. The lamb was the god for the Egyptians and so when they saw this it made them very angry but they could not utter a sound in protest.
Many miracles were performed at that time, so we refer to this day as Shabbat haGadol.
We have a custom on this shabbat to read a portion of the Haggadah which tells the story of the Exodus