This act of smearing blood on the doorposts to ward off the Angel of Death (and have the 10th plague pass-over these homes), is the precursor to the mezuzah: an object marking the boundary between Divinely protected and unprotected domains. SIZE: 5 1/5" long, 5/8" depth, 3/4" wide
The word "mezuzah" appears for the first time in the account of the Exodus from Egypt. Before the last plague (death of the Egyptian firstborn), G-d forewarned the Jewish people to mark their doorposts with the blood of the sacrificial lamb so that the forces of destruction would pass over their houses. The Torah says:
And they shall take of the blood and they shall put it on the two mezuzoth (doorposts) and on the lintel... For the Lord will pass through to smite the Egyptians, and when He seeth the blood upon the lintel, and on the two doorposts, the Lord will pass over the door, and He will not allow the destroyer to come in unto your houses to smite [you]. (Exodus 12:7, 23)
This is why the Holiday of the Exodus is called Passover.