Proverbs 15:20-21

A wise son, &c. See the note on chap. 10:1, where we have the same proverb. Folly is joy to him that is destitute of wisdom

He not only works wickedness, but takes pleasure in doing it; but a man of understanding walketh uprightly Hebrew, יישׁר לכת, directeth, or maketh straight, his going; that is, ordereth all his actions by the rule of God's word, and delights in so doing, as may be understood from the opposite clause.