What does Deuteronomy 25:19 mean?

When you're harvesting your fields and forget a bundle of grain, don't go back for it. Leave it for outsiders, orphans, and widows, so the Lord your God will bless you in everything you do. Deuteronomy 25:19 - Modern Text Bible

(God wants his people to be generous and mindful of those in need, promising blessing for their kindness.)