Deuteronomy 7:4

For they will turn away thy son from following me
From the pure worship of God, his word, statutes, and ordinances:

that they may serve other gods;
worship their idols; that is, the daughters of Heathens, married to the sons of Israelites, would entice them from the worship of the true God to idolatry; so the Targum of Jonathan; as Solomon's wives drew him aside: or "he will turn away thy son" ^F4; meaning, as Jarchi observes, that the son of an Heathen, that marries the daughter of an Israelite, will turn away the son born of her to idolatry, called here the grandfather's son; though Aben Ezra says this respects the son mentioned in the preceding verse, that is, the son married to an Heathen woman, and not to a son born in such marriage:

so will the anger of the Lord be kindled against you, and destroy thee
suddenly;
by some immediate judgment striking dead at once; there being nothing more provoking to God than idolatry, that being directly contrary to his being, nature, perfections, honour, and glory, of which he is jealous.