What does Deuteronomy 29:18 mean?

So be careful. Don’t let anyone here—no man, woman, family, or tribe—turn away from the Lord our God and chase after those nations’ gods. Don’t let any root of bitterness or rebellion grow up among you, poisoning everyone. Deuteronomy 29:18 - Modern Text Bible

(He warns against anyone secretly turning away from God, using the image of a poisonous root to show how one person's rebellion can harm the whole community.)