“….And you shall keep it for inspection until the fourteenth day of this month…” – Shemot 12:6

וְהָיָה לָכֶם לְמִשְׁמֶרֶת עַד אַרְבָּעָה עָשָׂר יוֹם לַחֹדֶשׁ הַזֶּה – שמות יב, ו

Bnei Yisrael were commanded to designate a lamb on the 10^th of Nissan to be slaughtered as the Pesach offering four days later. Rashi comments (on Shemos 12:6) that these four days of waiting were necessary because “the time for the Redemption had arrived… but Bnei Yisrael were steeped in idolatry.” To leave Egypt’s borders but to bring Egypt’s undesirable influences—”the shame of the Earth” (Beraishis 42:9)—with them would mean the Redemption was incomplete. The slaughtering of sheep—an Egyptian deity—for the Pesach sacrifice was the Jewish people’s means of rehabilitation.

But the Jews in Egypt had not only dabbled in idolatry, they were steeped in it. Therefore, a one-time act that renounced their previous obsession with idolatry was not enough to deprogram them from Egyptian influence—a longer process was required: the four days of inspection. Why four days?

We find that when Avraham was commanded by G-d to offer his son Yitzchak as a sacrifice, he headed out the very next morning to do G-d’s bidding, but he was only shown the place where Yitzchak would be sacrificed three days into his journey—i.e., four days after the initial command. Rashi (on Beraishis 22:4) explains that G-d delayed showing it to him immediately “so that people should not say that He confused him and confounded him suddenly, overwhelming his mind, and if Avraham had had time to think it over, he would not have done it.”

A person’s greatest passion is his children. Giving Avraham four days to contemplate parting with his child made it undisputable, when he ultimately lifted the knife over Yitzchak, that he did so completely sound of mind. This was clearly a calculated decision, not a thoughtless spurt of inspiration or confusion.

Therefore, to remove the shame of Egyptian influence from Bnei Yisrael, they were commanded not only to slaughter a sheep, but to start the process four days in advance, fully aware of what they were about to do. By slaughtering what they once considered a deity after four days of collected thought, they effectively and indisputably purged themselves of their idolatrous state of mind.

—Likkutei Sichos, vol. 16, pp. 117-119