In the book of Exodus, God’s law says when you buy a male Hebrew “servant“, you have to free him in the seventh year of servitude, unless he doesn’t want to be free. When you buy a female Hebrew servant, on the other hand, you don’t need to free her in the seventh year.1
But when the law is repeated in the book of Deuteronomy, this time it says you do have to let your Hebrew servants go free in the seventh year, whether they’re men or women.
Later, the last king of Judah decides that everyone in Jerusalem has to free all their male and female Hebrew slaves. When the people decide they don’t want to give up their slaves, Jeremiah (speaking for God) says that they’re breaking God’s law. He claims that the law says they have to free all Hebrew slaves in the seventh year, not just the men.