Quick answer
Righteous speech is food, and it feeds crowds; the fool cannot even feed himself, and dies hungry for the one thing he would not take in.
Read both lines
The chapter has already called righteous speech a well (10:11) and silver (10:20); now it is bread. "Feed many" is shepherd language, the word for pasturing a flock, and it quietly enlarges the claim: a righteous person's words are not just occasionally helpful but sustaining, something a whole circle of people live on. Counsel, encouragement, truth told kindly, the right word in season: many are fed from lips like these, usually more than the speaker ever knows.
The second line lands with tragic irony. The fool, surrounded by this food, dies "for lack of wisdom," literally for lack of heart. Nourishment was available; the well was public; the bread was free. What he lacked was not access but appetite, the receiving heart this chapter keeps returning to (10:8, 10:17). You can starve at a banquet if you refuse to eat.
From this side of the cross
The table is full and the food is free. The fool's tragedy is not that wisdom withheld itself, but that he refused what was already offered.
Related: Proverbs 10:11 · Proverbs 9:1–6 · Proverbs 15:4
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.