Albert Barnes Commentary Exodus 12:7

"And they shall take of the blood, and put it on the two side-posts and on the lintel, upon the houses wherein they shall eat it." — Exodus 12:7 (ASV)

The upper door post - Or lintel, (Exodus 12:23). This direction was understood by the Hebrews to apply only to the first Passover: it was certainly not adopted in Palestine. The meaning of the sprinkling of blood is hardly open to question. It was a representation of the offering of the life, substituted for that of the firstborn in each house, as an expiatory and vicarious sacrifice.