John Gills Exposition of the Bible Commentary - Proverbs 20:30
The blueness of a wound cleanseth away evil ,.... Rubs it off and scours it away, as the word F13 תמריק "abstesio", Piscator, Mercerus, Cocceius; "detersio", Montanus, Michaelis; "effricatio", Schultens. 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 F14 ברע "in malo, sub, homine", Vatablus, Mercerus,... read more
Matthew Henry's Complete Commentary - Proverbs 20:30
Note, 1. Many need severe rebukes. Some children are so obstinate that their parents can do no good with them without sharp correction; some criminals must feel the rigour of the law and public justice; gentle methods will not work upon them; they must be beaten black and blue. And the wise God sees that his own children sometimes need very sharp afflictions. 2. Severe rebukes sometimes do a great deal of good, as corrosives contribute to the cure of a wound, eating out the proud flesh. The... read more