Matthew Henry Presbyterian @wholebiblehenry

Solomon had commended eloquence, or the sweetness of the lips (Pro 16:21), 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.

John Gill Reformed Baptist @doctorgill

The heart of the wise teacheth his mouth,.... That is, a man that is wise in heart, as in Pro 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...

Jamieson-Fausset-Brown Reformed @jfbcommentary

The heart is the source of wisdom flowing from the mouth.