77. We have learnt the secret meaning of it. It is written, "And take a bunch of hyssop, and dip it in the blood that is in the basin, and touch with it the lintel and two side posts..." (Shemot 12:22). HE ASKS, Why a bunch of hyssops? HE ANSWERS, In order to destroy the Impure Spirit from among them and to indicate on their houses at these three places the Complete Faith, one on this side and one on that side - ON THE TWO SIDE POSTS THAT ALLUDE TO THE TWO COLUMNS, RIGHT AND LEFT - and one between them ON THE LINTEL THAT ALLUDES TO THE CENTRAL COLUMN. Therefore, "Hashem will pass over the door, and will not allow the Destroyer to come into your houses to smite you" (Ibid. 23), for He sees the Holy Name marked on the entrance, WHICH IS THE SECRET OF THE THREE COLUMNS.
189. When the Holy One, blessed be He, came to Egypt, He saw how the blood of the Passover that was marked on the entrance and the blood of the circumcision were on the door, as it is written, "And take a bunch of hyssop, and dip it in the blood that is in the basin, and touch with it..." (Shemot 12:22). We have explained that hyssop removes evil spirits and any aspect of a bad odor when it is operative for the supernal redemption of Yisrael.