The Mekhilta raises a question that cuts to the heart of the Passover story: why did God command the Israelites to select the Passover lamb four full days before slaughtering it? Why the wait?
The answer reveals something uncomfortable about Israel's spiritual state in Egypt. According to the Mekhilta, the Israelites had sunk deep into idolatry during their centuries of bondage. This was not a minor lapse. Idolatry, the text explains, is equivalent to transgressing all of the commandments at once, as Scripture indicates: "And if from the eyes of the congregation it were done unwittingly" (Numbers 15:24) — a verse the rabbis read as singling out idol worship as the one transgression that carries the weight of every other.
So when the time came for redemption, the Israelites had a problem. They had accumulated no merit. They had nothing to show for themselves spiritually. God, in His mercy, gave them a commandment they could perform immediately — selecting the Passover lamb. But He built in a four-day waiting period, during which the lamb had to be kept and inspected.
Those four days were not about the lamb. They were about the people. The act of selecting an animal that the Egyptians worshipped as a god, tying it to the bedpost in full view of their neighbors, and waiting — that required courage. It required a public break with the idolatry they had absorbed. The four days of "keeping" the lamb were really four days of spiritual preparation, a bridge between slavery and freedom, between the person each Israelite had become in Egypt and the person God needed them to be.