John Gill, on Prov 20:30

The blueness of a wound cleanseth away evil,.... Rubs it off and scours it away, as the word (m) signifies, or is a clearing and rubbing it off; some men must be beaten black and blue, or must have very sore correction, before they can be reclaimed and reformed from their evil ways; so some interpret it of the evil man (n): sanctified afflictions to God's people are the means of purging away their iniquities, their dross, and their sin; but there is nothing so effectually cleanses from sin as the blood of Jesus, or heals or cures of it as his blue wounds and stripes; see Isa 27:9; so do stripes the inward part of the belly; or heart and conscience; by means of corrections and chastisement men are brought to an inward sense of sin; they are shown their transgressions wherein they have exceeded, and are commanded to return from iniquity, Job 36:9; they lament and mourn over sin, confess it and forsake it; and then may the inwards of the heart, the mind and conscience, defiled with them, be said to be cleansed from them; especially when led by these stripes and corrections to the stripes, wounds, and blood of Christ which, being applied, cleanse from all, sin inwardly and outwardly. (m) "abstesio", Piscator, Mercerus, Cocceius; "detersio", Montanus, Michaelis; "effricatio", Schultens. (n) "in malo, sub, homine", Vatablus, Mercerus, Gejerus, Michaelis; "in malo (homine nequam)", Schultens, so Aben Ezra. Next: Proverbs Chapter 21