And the blood on the houses where you are staying shall be a sign for you: when I see the blood I will pass over you, so that no plague will destroy you when I strike the land of Egypt.
For God, when going through to smite the Egyptians, will see the blood on the lintel and the two doorposts, and God will pass over the door and not let the Destroyer enter and smite your home.
Does Hashem need to “look” in order to know if there is blood on the doorpost?
The Mechilta offers that this “seeing” hints at something beneath the surface. Hashem saw the blood of Akeidat Yitzchak along with the blood of the Pesach, reminiscent of Avraham’s calling Mount Moriah בהר ה’ יראה following the Akeida.
Bnei Yisrael wish to benefit from the merit of our Avot. When Yaakov prepares to meet Esav, he addresses Hashem as Elokei Avi Avraham v’Elokrei Avi Yitzchak. How will that be effective? Wasn’t Esav also a descendant?
Shem Mishmuel explains that in order to invoke “zchut Avot” one must follow in their footsteps. Yaakov did, while Esav less so. By taking the sheep, representing Egyptian idol worship, on the tenth of Nisan, shechting and displaying the blood, Bnei Yisrael expressed a communal mesirat nefesh, as Abraham and Isaac did centuries earlier.
Thrice a day we declare: וזוכר חסדי אבות ומביא גואל לבני בניהם.
If we would like to benefit from chsdei avot, we had better walk in their path.