The heart of the wise teacheth his mouth. Out of the abundance of his heart the wise man speaks; the spirit within him finds fit utterance. Pectus est quod disertos facit. The thought and mind control the outward expression and make it eloquent and persuasive (comp.
Proverbs 15:2). And addeth learning to his lips; Vulgate, "addeth grace." But lekach, which means properly "reception," "taking in," is best rendered "learning," as in Proverbs 16:21; Proverbs 1:5, etc.
The intellect and knowledge of the wise display themselves in their discourse. Delitzsch, "Learning mounteth up to his lips." Ec Proverbs 21:26, "The heart of fools is in their mouth; but the mouth of the wise is in their heart."
Septuagint, "The heart of the wise will consider what proceedeth from his mouth; and on his lips he will carry prudence ( ἐπιγνωμοσύνην)."