Psalms 51:7

I. See here what David prays for. Many excellent petitions he here puts up, to which if we do but add, "for Christ's sake," they are as evangelical as any other. 1. He prays that God would cleanse him from his sins and the defilement he had contracted by them (Psa 51:7): "Purge me with hyssop; that is, pardon my sins, and let me know that they are pardoned, that I may be restored to those privileges which by sin I have forfeited and lost." The expression here alludes to a ceremonial distinction, that of cleansing the leper, or those that were unclean by the touch of a body by sprinkling water, or blood, or both upon them with a bunch of hyssop, by which they were, at length, discharged from the restraints they were laid under by their pollution. "Lord, let me be as well assured of my restoration to thy favour, and to the privilege of communion with thee, as they were thereby assured of their re-admission to their former privileges." But it is founded upon gospel-grace: Purge me with hyssop, that is, with the blood of Christ applied to my soul by a lively faith, as water of purification was sprinkled with a bunch of hyssop.

— Matthew Henry's Concise Commentary (public domain)

A series of prayers for forgiveness and purifying. Purge . . . hyssop--The use of this plant in the ritual (Exo 12:22; Num 19:6, Num 19:18) suggests the idea of atonement as prominent here; "purge" refers to vicarious satisfaction (Num 19:17-20).

— Jamieson-Fausset-Brown Commentary (public domain)