Bridges on Proverbs 20:30
Charles Bridges on Proverbs 20:30

30.  The blueness of a wound cleanseth away evil: so do stripes the inward parts of the belly. {cleanseth...: Heb. is a purging medicine against}
Chastisement is the LORD’s ordinance — the pain of the flesh for the subjugation of the spirit; sometimes even “the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.” (1 Corinthians 5:5.) It describes not the gentle stroke, but the severity of parental discipline; not in pleasure or caprice, much less in anger, but for profit. (Hebrews 12:10.) The diseased body needs medicine no less than food, and indeed to give nourishment. The diseased soul needs chastening no less than consolation, and as the main preparation for consolation. But if the blueness of the wound — the mark of severe chastisement — cleanseth away evil, is it not the lesser evil, as the means of subduing the greater? Do not the Lord’s stripes cleanse the inward parts? Misery beyond measure miserable is the untamed stubbornness of self-will. A gentle stroke is first tried. When this remedy is ineffectual, the blueness of the wound is needful. Manasseh’s Babylonish chains doubtless prevented the “everlasting chains of darkness.”† Similar discipline was effectual with the holy nation, the prodigal son,† and the incestuous Corinthian.† Multitudes have borne witness to the love, wisdom, and power of their Father’s discipline — “chastened of the Lord, that they might not be condemned with the world.”† The evil was cleansed away; and those, who groaned under the stripes, to all eternity will tune their harps to the song — “I know, O LORD, that thy judgments are right, and that thou in faithfulness hast afflicted me.” (Psalm 119:75.)
Child of God! Think of your Father’s character. “He knoweth your frame. He doth not afflict willingly.” (Ib. 103:14. Lamentations 3:33.) Nothing will be given in weight or measure beyond the necessity of the case.† But truly blessed are the stripes, that humble and break the proud will.† Rich indeed are “fruits of righteousness” from the conflict and suffering of the flesh.†