| Clarke's Commentary on the Bible The heart of the wise teacheth his mouth - He has a wise heart; he speaks as it dictates; and therefore his speeches are all speeches of wisdom.
Gill's Exposition of the Entire BibleThe heart of the wise teacheth his mouth,.... That is, a man that is wise in heart, as in Proverbs 16:21; his heart will teach his mouth what to say, when to say it, and before whom; it will prompt him to matter, that he shall not be at a loss what to say, nor how to say; it will furnish him with words and things; out of the abundance of the heart the mouth speaketh, Matthew 12:34; and addeth learning to his lips: so that he does not deliver out mere words, but solid learning along with them, instructive to himself and others. The Targum is, "and by his lips he addeth doctrine;'' or increases knowledge.
Keil and Delitzsch Biblical Commentary on the Old Testament23 The heat of the wise maketh his mouth wise, And learning mounteth up to his lips. Regarding השׂכּיל as causative: to put into the possession of intelligence, vid., at Genesis 3:6. Wisdom in the heart produceth intelligent discourse, and, as the parallel member expresses it, learning mounteth up to the lips, i.e., the learning which the man taketh into his lips (Proverbs 22:18; cf. Psalm 16:4) to communicate it to others, for the contents of the learning, and the ability to communicate it, are measured by the wisdom of the heart of him who possesses it. One can also interpret הוסיף as extens. increasing: the heart of the wise increaseth, i.e., spreads abroad learning, but then בּשׂפתיו (Psalm 119:13) would have been more suitable; על־שׂפתיו calls up the idea of learning as hovering on the lips, and thus brings so much nearer, for הוסיף, the meaning of the exaltation of its worth and impression.
Geneva Study BibleThe heart of the wise teacheth his mouth, and addeth learning to his lips.
Wesley's Notes 16:23 Teacheth - Directs him what to speak, and keeps him from speaking foolishly. Addeth - Enables him to speak learnedly and wisely.
King James Translators' Notesteacheth: Heb. maketh wise
Jamieson-Fausset-Brown Bible Commentary23. The heart is the source of wisdom flowing from the mouth.
Matthew Henry's Concise Commentary16:12. The ruler that uses his power aright, will find that to be his best security. 13. Put those in power who know how to speak to the purpose. 14,15. Those are fools, who, to obtain the favour of an earthly prince, throw themselves out of God's favour. 16. There is joy and satisfaction of spirit, only in getting wisdom. 17. A sincerely religious man keeps at a distance from every appearance of evil. Happy is the man that walks in Christ, and is led by the Spirit of Christ. 18. When men defy God's judgments, and think themselves far from them, it is a sign they are at the door. Let us not fear the pride of others, but fear pride in ourselves. 19. Humility, though it exposes to contempt in the world, is much better than high-spiritedness, which makes God an enemy. He that understands God's word shall find good. 21. The man whose wisdom dwells in his heart, will be found more truly prudent than many who possess shining talents. 22. As waters to a thirsty land, so is a wise man to his friends and neighbours. 23. The wise man's self-knowledge, always suggests something proper to be spoken to others. 24. The word of God cures the diseases that weaken our souls. 25. This is caution to all, to take heed of deceiving themselves as to their souls. 26. We must labour for the meat which endureth to everlasting life, or we must perish.
Matthew Henry's Whole Bible CommentaryVerse 23 Solomon had commended eloquence, or the sweetness of the lips (v. 21), and seemed to prefer it before wisdom; but here he corrects himself, as it were, and shows that unless there be a good treasure within to support the eloquence it is worth little. Wisdom in the heart is the main matter. 1. It is this that directs us in speaking, that teaches the mouth what to speak, and when, and how, so that what is spoken may be proper, and pertinent, and seasonable; otherwise, though the language be ever so fine, it had better be unsaid. 2. It is this that gives weight to what we speak and adds learning to it, strength of reason and force of argument, without which, let a thing be ever so well worded, it will be rejected, when it comes to be considered, as trifling. Quaint expressions please the ear, and humour the fancy, but it is learning in the lips that must convince the judgment, and sway that, to which wisdom in the heart is necessary. | 
