The Mekhilta completes its trilogy of faith-based miracles with the blood of the Passover lamb. God told the Israelites to slaughter a lamb and place its blood on their doorposts, declaring: "And the blood shall be for you as a sign" (Exodus 12:13). When the destroying angel passed through Egypt that night, it would "skip over" any door marked with blood.
The Mekhilta asks the same question it posed about Moses' raised hands and the bronze serpent: "How can the blood affect an angel, or Israel?" Blood is a physical substance. An angel is a spiritual being. There is no logical mechanism by which lamb's blood on a wooden doorframe could repel a heavenly destroyer.
The answer, once again, is faith. When Israel performed the act — when they slaughtered the lamb, collected the blood, and smeared it on their doors exactly as God commanded — they demonstrated total trust in His word. They did something that made no rational sense as a defense against supernatural destruction. And because they did it, "the Holy One Blessed be He pitied them," and "the Lord skipped over the door" (Exodus 12:23).
Three episodes, one principle. Moses' hands did not win the battle. The bronze serpent did not cure the venom. The blood did not repel the angel. In each case, the physical act was a container for something invisible — the faith of the people and the mercy of God. The Mekhilta teaches that obedience to a divine command, even when its logic is opaque, is itself the miracle.