Moreover, they shall take some of the blood and put it on the two doorposts and on the lintel of the houses in which they eat it. (Exodus 12:7)
Moses commanded the children of Israel to mark their homes with the blood of the Passover lambs. They were to dip hyssop into the blood and smear it on their doorposts. Although Passover was thereafter celebrated annually, the Israelite homes were never again smeared with blood from the Passover lambs. The smearing with blood was a one-time ritual. Every Passover thereafter, the blood of the Passover lambs was splashed on the altar in the Tabernacle/Temple as a remembrance of the plague of the firstborn and the blood on the doorposts of Israelite homes in Egypt.
Try to imagine the Passover in the Temple on the day the Master died. While His precious body hung dying on the cross, a short distance outside the city walls pilgrims were flooding the Temple courts, leading their lambs to slaughter. While His blood stained the stones beneath the cross, the priesthood of Israel was splashing basin after basin of Passover blood against the stones of the Temple altar. While the women wept at the foot of the cross, the Levites in the Temple courts were chanting the songs of the Hallel: Psalms 113-119. Once slaughtered, the lambs in the Temple were hung from iron hooks in crucifixion poses for skinning, and once skinned, they were bound by the hooves, hand and foot as it were, to wooden poles, to be carried from the Temple on the backs of the worshippers. Meanwhile, the Master hung in crucifixion pose from iron nails, bound hand and foot to a wooden pole.
Believers have traditionally interpreted the Passover blood on the doorway as a symbol of Messiah's blood. Consider a few of the parallels. Messiah is called our Passover Lamb. He died at Passover time. Just as the death came upon Egypt to claim the firstborns, so too all mankind is given over to death. Just as those under the protection of the Passover lamb's blood markings were protected from death, so too those who take refuge under the blood of Messiah are protected from condemnation. They are given eternal life and will overcome death in the resurrection.
What is more, Messiah's blood marked the soil of Jerusalem, the city in which the Holy Temple is located. According to Jewish tradition, Jerusalem and the Temple therein are called the "gateway to heaven." It is as if Messiah's blood was smeared upon the doorposts of heaven.