Psalms 51:7

Again David pleaded for purification and cleansing (Psalms 51:1-2). In Israel, the priest sprinkled animal blood on the altar with a hyssop branch. This ritual symbolized cleansing by sacrificial death (cf. Hebrews 9:22). If God would wash David morally, he would be thoroughly clean.

"Cleansing in Scripture is twofold: (1) of a sinner from the guilt of sin-the blood (hyssop) aspect; and (2) of a saint from the defilement of sin-the water (wash) aspect. Under grace the sinner is purged by blood when he believes (Matthew 26:28; Hebrews 1:3; Hebrews 9:12; Hebrews 10:14). Both aspects of cleansing, by blood and by water, are brought out in John 13:10; Ephesians 5:25-26 . . ." [Note: The New Scofield . . ., pp. 624-25.]