Another matter, “you shall take a bunch of [agudat] hyssop,” – in other words, I will render you an association [aguda] for Myself, even though you are lowly like the hyssop, as it is stated: “And you will be My treasure from all the peoples” (Exodus 19:5). “And dip it in the blood that is in the basin.” What did the Holy One blessed be He see [that led Him] to protect them with blood? It was in order to evoke for them the blood of Abraham’s circumcision.
It was with two bloods that Israel was rescued from Egypt; the blood of the paschal offering and the blood of circumcision, as it is stated: “I said to you: With your blood, live; I said to you: With your blood, live” (Ezekiel 16:6) – with the blood of the paschal offering and the blood of circumcision. “And touch the lintel,” – due to the merit of Abraham; “and on the two doorposts,” – due to the merit of Isaac and Jacob.
Due to their merit, He will see the blood “and will not allow the destroyer to come to your houses to smite you” (Exodus 12:23).