Imagine a marriage vow broken by infidelity. That's the picture Jeremiah paints when he talks about God's covenant with His people.
The core of this verse is the accusation that 'The house of Israel and the house of Judah have broken my covenant.' This covenant wasn't just a contract; it was God's solemn promise to be their God, and their promise to be His people, living under His rule. The 'iniquities' they returned to were directly linked to breaking this sacred bond. By 'going after other gods to serve them,' they were engaging in the ultimate betrayal. Idolatry, the worship of anything other than the one true God, was seen as spiritual adultery, a direct violation of the covenant that bound them exclusively to Yahweh.