What does Proverbs 10:20 mean?

There is a contrast between the words of a person pursuing godliness versus those of a person seeking selfish interests.

The righteous person's words are extremely valuable. In prior passages, Solomon depicted wisdom as a woman who claimed this same value for her teachings (Proverbs 8:18–21). Wise words point the way to life, both eternal life and daily life. They encourage, comfort, and provide excellent counsel. Out of the good treasure of his heart the righteous person produces good (Luke 6:45). His lips speak God's words that "are pure words, like silver refined in a furnace on the ground, purified seven times" (Psalm 12:6). The righteous person's words are true and trustworthy, like God's Word (John 17:17).

The heart of the wicked is of no eternal worth. It produces evil (Luke 6:45). The wicked person curses, blasphemes, lies, slanders, defames, gossips, and destroys. His words tear down, whereas the words of the righteous person build others up. Endless chatter of evil words (Proverbs 10:19) contrasts sharply with the wisely chosen words of the righteous person.

The following verse uses similar imagery: referring to the benefits of godly wisdom as spoken by wise people (Proverbs 10:21).