John Gill Commentary Proverbs 16:23

"The heart of the wise instructeth his mouth, And addeth learning to his lips." — Proverbs 16:23 (ASV)

The heart of the wise teaches 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 speaks, (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.