Purge me with hyssop, and I shall be clean: wash me, and I shall be whiter than snow.
Read Chapter 51
Augustine of Hippo
12. "Thou shall sprinkle me," he saith, "with hyssop, and I shall be cleansed" (ver. 7). Hyssop we know to be a herb humble but healing: to the rock it is said to adhere with roots. Thence in a mystery the similitude of cleansing the heart has been taken. Do thou also take hold, with the root of thy love, on thy Rock: be humble in thy humble God, in order that thou mayest be exalted in thy glorified God. Thou shalt be sprinkled with hyssop, the humility of Christ shall cleanse thee. Despise not the herb, attend to the efficacy of the medicine. Something further I will say, which we are wont to hear from physicians, or to experience in sick persons. Hyssop, they say, is proper for purging the lungs. In the lung is wont to be noted pride: for there is inflation, there breathing. It was said of Saul the persecutor as of Saul the proud, that he was going to bind Christians, breathing slaughter: he was breathing out slaughter, breathing out blood, his lung not yet cleansed. Hear also in thi...
Hyssop, which was used in sprinkling lepers, (Leviticus xiv. 6.) not that the like ceremony, or even sacrifice, would suffice to heal the wound of the soul. Sincere contrition, (ver. 18, 19.) and the virtue of Christ's blood, are necessary. (Calmet) (Hebrews ix. 19.)
The heat (Numbers xix.) and operation of this sovereign medicine was shown to the prophet, John xix. (Worthington)
The sprinkling of the priest might be of service, if the heart was contrite, Hebrews ix. 13. (Menochius)