Judah in the south had witnessed everything in the north that the Lord is asking Jeremiah to remember. She had seen northern Israel’s unfaithfulness and more to the point, she had seen the judgment that followed as the Lord sent faithless Israel away with a divorce decree.
This continues the comparison of the covenant relationship to marriage that started with the question in Jeremiah 3:1. The grounds for the divorce was Israel’s ongoing spiritual adulteries.
The Hebrew root here is naap, which is used in the Ten Commandments (Exodus 20:14) to refer to the breaking of the marriage bond, specifically through sexual activity with someone else’s spouse.1
7 And I thought, ‘After she has done all this she will return to me,’ but she did not return, and her treacherous sister Judah saw it.