Matthew Henry Commentary Proverbs 27:22

"Though thou shouldest bray a fool in a mortar with a pestle along with bruised grain, Yet will not his foolishness depart from him." — Proverbs 27:22 (ASV)

Some are so bad that even severe methods do not fulfill the purpose; what remains but that they should be rejected? The new-creating power of God's grace alone is able to make a change.