He that hath knowledge spareth his words: and a man of understanding is of an excellent spirit.

King James Translators' Notes

an...: or, a cool

Jamieson-Fausset-Brown Bible Commentary

27, 28. Prudence of speech is commended as is an excellent or calm spirit, not excited to vain conversation.

Matthew Henry's Concise Commentary

17:19. If we would keep a clear conscience and a quiet mind, we must shun all excitements to anger. And a man who affects a style of living above his means, goes the way to ruin. 20. There is nothing got by ill designs. And many have paid dear for an unbridled tongue. 21. This speaks very plainly what many wise and good men feel very strongly, how grievous it is to have a foolish, wicked child. 22. It is great mercy that God gives us leave to be cheerful, and cause to be cheerful, if by his grace he gives us hearts to be cheerful. 23. The wicked are ready to part with their money, though loved, that they may not suffer for their crimes. 24. The prudent man keeps the word of God continually in view. But the foolish man cannot fix his thoughts, nor pursue any purpose with steadiness. 25. Wicked children despise the authority of their father, and the tenderness of their mother. 26. It is very wrong to find fault for doing what is duty. 27,28. A man may show himself to be a wise man, by the good temper of his mind, and by the good government of his tongue. He is careful when he does speak, to speak to the purpose. God knows his heart, and the folly that is bound there; therefore he cannot be deceived in his judgment as men may be.

Matthew Henry's Whole Bible Commentary

Verses 27-28

Two ways a man may show himself to be a wise man:- 1. By the good temper, the sweetness and the sedateness, of his mind: A man of understanding is of an excellent spirit, a precious spirit (so the word is); he is one that looks well to his spirit, that it be as it should be, and so keeps it in an even frame, easy to himself and pleasant to others. A gracious spirit is a precious spirit, and renders a man amiable and more excellent than his neighbour. He is of a cool spirit (so some read it), not heated with passion, nor put into any tumult or disorder by the impetus of any corrupt affection, but even and stayed. A cool head with a warm heart is an admirable composition. 2. By the good government of his tongue. (1.) A wise man will be of few words, as being afraid of speaking amiss: He that has knowledge, and aims to do good with it, is careful, when he does speak to speak to the purpose, and says little in order that he may take time to deliberate. He spares his words, because they are better spared than ill-spent. (2.) This is generally taken for such a sure indication of wisdom that a fool may gain the reputation of being a wise man if he have but wit enough to hold his tongue, to hear, and see, and say little. If a fool hold his peace, men of candour will think him wise, because nothing appears to the contrary, and because it will be thought that he is making observations on what others say, and gaining experience, and is consulting with himself what he shall say, that he may speak pertinently. See how easy it is to gain men's good opinion and to impose upon them. But when a fool holds his peace God knows his heart, and the folly that is bound up there; thoughts are words to him, and therefore he cannot be deceived in his judgment of men.