What does Proverbs 13:21 mean?

Solomon contrasts what generally happens to those who disobey God versus those who honor Him. Those who pursue evil encounter God's wrath, as well as the natural consequences of things like deceit, greed, and violence (Proverbs 12:13; 13:5). Scripture acknowledges that such people may seem to thrive, for a while (Psalm 73:2–3), but there is a terrible end for their rebellion (Proverbs 11:7; Revelation 20:11–15). Romans 6:23 assures us that "the wages of sin is death," and Isaiah 48:22 declares, "'There is no peace,' says the Lord, 'for the wicked.'"

However, the righteous enjoy God's peace. The psalmist testifies: "Great peace have those who love your law; nothing can make them stumble" (Psalm 119:165). Retribution awaits those who pursue an evil life, but rewards await those who lead a righteous life. Galatians 6:8 teaches that "the one who sows to his own flesh will from the flesh reap corruption, but the one who sows to the Spirit will from the Spirit reap eternal life." Knowing this principle of reciprocity, Paul encourages the Galatians not to "grow weary of doing good, for in due season we will reap, if we do not give up" (Galatians 6:9).

While godly, righteous people may experience pain and suffering in the world (John 16:33), that is not the end of their story (Romans 8:18). In general, doing good leads to good outcomes, and sin brings natural, negative consequences. The person who lives an evil life will be forever running from the results of their own actions.