Matthew Henry Commentary Proverbs 17:27-28

"He that spareth his words hath knowledge; And he that is of a cool spirit is a man of understanding. Even a fool, when he holdeth his peace, is counted wise; When he shutteth his lips, he is [esteemed as] prudent." — Proverbs 17:27-28 (ASV)

A man may show himself to be a wise man, by the good temper of his mind, and by the good control of his tongue. He is careful when he speaks, to speak to the point. God knows his heart, and the folly that is bound there; therefore He cannot be deceived in His judgment as humans may be.