What does Deuteronomy 29:15 mean?

that you may enter into the covenant of Yahweh your God, and into his oath, which Yahweh your God makes with you today;

that he may establish you today as his people, and that he may be your God, as he spoke to you, and as he swore to your fathers, to Abraham, to Isaac, and to Jacob.

Neither do I make this covenant and this oath with you only,

(for you know how we lived in the land of Egypt, and how we came through the middle of the nations through which you passed;

and you have seen their abominations, and their idols, wood and stone, silver and gold, which were among them);

lest there should be among you man, woman, family, or tribe whose heart turns away today from Yahweh our God, to go to serve the gods of those nations; lest there should be among you a root that produces bitter poison;