John Gill, on Prov 16:23

“The heart of the wise shall instruct his mouth: and shall add grace to his lips.”

“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 things; out of the abundance of the heart the mouth speaketh, Mat 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.”

Imported from an open dataset — not yet checked against the printed edition.