What does Deuteronomy 31:21 mean?

When disaster and trouble come, this song will remind them of what happened. It won't be forgotten by their descendants. I know what they're planning to do, even before they enter the land I promised them.' Deuteronomy 31:21 - Modern Text Bible

(God says the song will stick with them and their kids, reminding them of the truth, even when things go wrong.)