C. F. Keil and Franz Delitzsch on Proverbs 20:15

Pro 20:15 15 There is indeed gold, and many pearls;      But a precious treasure are lips full of knowledge.

In order to find a connection between this proverb and that which precedes, we need only be reminded of the parable of the merchantman who sought goodly pearls, Mat 13:45. The proverb rises to a climax: there is gold, and there are pearls in abundance, the one of which has always a higher value than the other; but intelligent lips are above all such jewels - they are a precious treasure, which gold and all pearls cannot equal. In a similar manner the N.T. places the one pearl above the many goodly pearls. So might דעת (chokma) be called the pearl above all pearls (Pro 3:15; Pro 8:11); but the lips as the organ of knowledge are fittingly compared with a precious vessel, a vessel of more precious substance than gold and pearls are.