Proverbs 16:21

The wise in heart shall be called prudent: and the sweetness of the lips increaseth learning.

Wisdom that dwells in the heart is recognized as prudence. Gracious, sweet speech increases learning. Pleasantness of the lips makes teaching more effective, so that learning is enlarged in those who hear. Inner wisdom and outward speech thus belong together, with the wise heart expressing itself in words that help others learn.