When one reads through Shmot Chapter 12, it becomes quite clear that blood will play a significant role in bringing about the salvation of the Hebrew slaves at the midnight hour when Egypt will be struck its most devastating blow.

Verses 7, 13, 22 and 23, when run together, read something like this.

“They must take the blood and place it on the two doorposts and on the beam above the door of the houses in which they will eat [the sacrifice]. The blood will be a sign for you on the houses where you are staying. I will see the blood and pass you by (pasach). There will not be any deadly plague among you when I strike Egypt. {Instructions to the elders are to tell the people to] ‘Take a bunch of hyssop and dip it into the blood that [will be placed] in a basin. Touch the beam over the door and the two doorposts with some of the blood in the basin. Not a single one of you may go out the door of his house until morning. God will then pass through to strike Egypt. When he sees the blood over the door and on the two doorposts, God will pass over that door, and not let the force of destruction enter your houses to strike.’”

The Ktav V’Hakabalah asks a seemingly obvious question. Does God really need the blood as a sign? If He wants to distinguish between the Egyptians who suffer in the plague and the Israelites who are spared, could He not just say “My wonders will be proven by the fact that Egyptians will die and Israelites will not”?

Ibn Ezra rejects the notion that the blood was a derivative of a public process aimed at showing the Egyptians who is boss. Were it so, he argues, the blood would have been put on courtyard gates instead of on the doorway of homes recessed from the street and the slaughtering of the lamb would have taken place in the daytime, instead of closer to nighttime when people are already in their homes. Ibn Ezra even derives from “The blood will be a sign for you” that you, who cannot go outside all night, will be able to see the blood because it will be on the inside of your home.