Leviticus 14:4-7

And what he is doing here is he is asking these things of God because he sees God as his priest. He is the one that he would confess his uncleanness to. And He is the one, then, that would cleanse him from his defilement. If you would look in Leviticus 14:4-7, you will see there that lepers had to present themselves before the priest for purification. In Luke 5:12-14, this is what Jesus told the leper that he healed to do. In that ceremony of purification, the priest, satisfied that the leper had met all the requirements for purification, would take a bunch of hyssop (and hyssop is an aromatic plant similar to marjoram or perhaps thyme), and he would dip that in water and sprinkle that water on the person as an act, a ritual act of cleansing. And then he would declare the formerly unclean person to be clean.