When the Holy One Blessed Be He wanted to have unification with the Israelites in Egypt. It wasn’t the proper time because as the Zohar describes, “The foreskin covers the light”. The presence of the negative side as the Klipa (shell) blocked the Light of Chokmah that was needed to have a direct connection between God and his people. The unification was needed to separate them from the control of Egypt and to take them out to freedom. God sent the minister of the other side, Satan, to be busy with testing Job’s faith.
He rushed the Israelites out before Satan finish his deal with Job and come for them.
“וְכָכָה, תֹּאכְלוּ אֹתוֹ–מָתְנֵיכֶם חֲגֻרִים, נַעֲלֵיכֶם בְּרַגְלֵיכֶם וּמַקֶּלְכֶם בְּיֶדְכֶם; וַאֲכַלְתֶּם אֹתוֹ בְּחִפָּזוֹן, פֶּסַח הוּא לַיהוָה”
“Now you shall eat it in this manner: with your loins girded, your sandals on your feet, and your staff in your hand; and you shall eat it in haste– it is Passover for YHVH.”
The lamb was the aspect of the Egyptians God. The Israelites ordered to sacrifice lamb and eat it after it was roasted over fire to burn any negative aspect of desire from it.
The Matzah was also a tool to disconnect from the desire for the self that could’ve attracted the negative side and blocked the great light God revealed when they left Egypt.