Through the sacrifice, the Israelites demonstrate that they fear God more than they fear the Egyptians. Such obedience, according to this view, merits the deliverance of Passover night. But the blood marking the doors of the Israelites signifies much more than obedience. It involves substitution. In place of the life of the firstborn that God was requiring of each household in Egypt, he would accept the life of the lamb.
Substitution defines some of the most powerful scenes of Torah.
But God will permit a substitute to be offered in place of the firstborn of Israel. The ordinance of the firstborn, which immediately follows the account of the first Passover, builds on this truth. The firstborn belongs to the Lord because it is a substitute for the whole, and God is the source of all life. Israel as firstborn of the nations signifies that all the nations belong to the Lord. Israel is required to redeem or buy back the firstborn because it belongs to God.