What does Deuteronomy 23:20 mean?

You can charge interest to people from other nations, but not to your own people. If you do this, God will bless you in everything you do in the land he’s giving you. Deuteronomy 23:20 - Modern Text Bible

(The rule is different for outsiders, but among Israelites, generosity is expected. God promises to reward this kind of fairness and kindness.)