The most spiritually significant of the ritual uses of hyssop in the Old Testament is recorded in Exodus 12:22. Moses has just given the instructions for the killing of the Passover lamb, and he continues with some further instructions that must have been rather startling for those participating Israelites:
And you shall take a bunch of hyssop, dip it in the blood [of the Passover lamb] that is in the basin, and strike the lintel and the two doorposts with the blood that is in the basin. And none of you shall go out of the door of his house until morning.
It is important that we consider all the aspects of this event. During repeated requests by Moses for Pharaoh to allow Israel to leave Egypt, Pharaoh had continually refused to let God's people go, and the nation had endured nine plagues of cataclysmic consequences. The economy of the nation was largely in shambles. Crops were ruined, and disease had run rampant.
Since the third plague, God had also made readily visible a clear distinction between the captive nation of Israel and the Egyptians, in that the Israelites in Goshen had been spared much of the devastation that had ruined the rest of Egypt. By the use of the blood of the sacrificial lamb, God was about to make a final, absolute distinction between these two nations that would never be forgotten.
We must recognize that Egypt suffered the devastation at the hand of God because though it was a sophisticated, dazzling, world-dominating empire, it was also a wicked, idolatrous nation. The Egyptians were a people who openly flouted the natural evidence of a supreme Creator by worshipping a pantheon of idols and gods dedicated to their own passions and lusts. Egyptians regularly engaged in a frenzy of immoral and idolatrous celebrations, sporting events, fashions, and music all dedicated to gods of materialism and human gratification.
The plagues God meted upon the land of Egypt and its people were just as much attacks on her idols and lifestyle as they were punishments for the sins of her people. As just one example, the Egyptians worshipped the Nile River as a god, and when God turned its waters to blood, the life-giving nature of the river was destroyed, along with the power that the Nile River god supposedly possessed.
Thus, in this solemn Passover event of Exodus 12, God used blood of a different nature to represent the saving, life-giving power that only He, the almighty, eternal God, possessed. The sacrificial lamb of Passover symbolized the future Son of God, who would take upon Himself the role of the sacrificial Lamb of God (John 1:29). The shed blood of the Passover lamb symbolized the blood to be shed by the coming Messiah.
The bunch of hyssop was dipped into the blood, and per God's instructions, that blood was sprinkled or brushed on the doorposts and lintel of each home. The Israelites were then told to stay within those homes, separated from the Egyptian people and their normal routines. That night, there was to be no interaction or communication with any aspect of the Egyptian civilization. Their very lives depended on their following this command to the letter.
The sacrificial blood, sprinkled or smeared by the bunch of hyssop, graphically represented a separation and a protection of Israel against the deadly havoc that God wrought upon Egypt that night. The blood ceremonially cleansed and protected the people inside those homes against the plague of death that struck a people who practiced the filthy abominations of godlessness.
Later, in the books of Leviticus and Numbers, hyssop was used as part of sacrificial ceremonies. The hyssop was always tied into bunches for use in sprinkling the blood of the sacrificed animal. In some sacrifices, the priest sprinkled the blood onto the person making the sacrifice.
In Numbers 19, Moses gives instructions for one who is unclean due to touching a dead body. These instructions include taking a bunch of hyssop, dipping it into clean, running water, and sprinkling the unclean individual, his tent, and possessions. This example clearly connects the use of hyssop and clean water for cleansing.
Over the years, some have suggested that hyssop contains valuable antiseptic or cleansing properties that would "disinfect" the contaminated person or his possessions. This cannot be the point because such an idea contradicts the fact that God is the only Source of true purification. The biblical use of hyssop in the Passover, the sacrifices, and the ceremonial cleansing rituals was a constant reminder, painting a detailed picture of the washing, cleansing, saving, purification, and salvation from death itself that come only from the eternal God.
Purge Me With Hyssop