What does Psalm 37:21 mean?

One of the distinguishing marks of a wicked person is his lack of trustworthiness. This is symbolized by David as a person who borrows but does not pay back what is owed. In contrast, a righteous person not only meets their obligations, they practice generosity. Sin leads a person to selfishly take from others; godliness encourages charity and kindness.

The righteous have what they need, because God blesses them, and therefore they can give to others. God promised to reward Israel's faithfulness by making it possible for the Israelites to lend to many nations (Deuteronomy 15:6). He repeated this promise in Deuteronomy 28:12. So far as literal material prosperity is concerned, this promise does not extend to every believer in every period of history. It was given to the nation of Israel and was conditioned on Israel's faithfulness to the Lord. It is, therefore, a generalization, as is much of the advice in the book of Proverbs.

However, verses such as this show clearly that God frowns on untrustworthiness but smiles on generosity. Second Corinthians 9:11 teaches us that God enriches us for a reason: so that we may be generous in every way.