What does Deuteronomy 31:16 mean?

The Lord said to Moses, 'You're about to die, and these people will soon turn away and chase after the foreign gods of the land they're entering. They'll abandon me and break the agreement I made with them.' Deuteronomy 31:16 - Modern Text Bible

(God warns Moses that after he's gone, the people will turn away and break their commitment to him.)