The First Book of Kings describes ezob was a small plant. It was burned with the red Heifer in Numbers xix. 6; and used for purification of lepers in Leviticus xiv. 4, 6, 49, 51; and Numbers xix. 18). At Passover it was used to sprinkle the blood of the sacrificial lamb on the doorposts (Ex. xii. 22). Its main use in biblical times was for religious purification.
The Gospel of John mentions that hyssop and vinegar were given to alleviate the thirst of Jesus during his Passion. Matthew and Mark refer to the plant simply as a reed or stick. In the Psalms the sprinkling of hyssop is used allegorically to refer to purification of the heart.
The Roman Catholic Church, and also some other sects have adopted the biblical practice of sprinkling with hyssop to sprinkling with water to ritually cleanse religious objects and people in a ritual called aspersion.