Albert Barnes Commentary Proverbs 20:30

"Stripes that wound cleanse away evil; And strokes [reach] the innermost parts." — Proverbs 20:30 (ASV)

Better, The blueness of a wound is a cleansing of evil, so are the stripes that go down to the inward parts of the belly.

The open sores of wounds left by the scourge, unclean and foul as they seem, are yet a cleansing, purifying process for evil; so also are the stripes that reach the inward parts of the belly, that is, the sharp reproofs, the stings of conscience, which penetrate where no scourge can reach, into the inner life of man. Chastisement, whatever its nature, must be real; the scourge must leave its mark, the reproof must go deep.