God tells Jeremiah to go to the gates of Jerusalem and tell people to change their ways.
They shouldn't feel safe just because they're in the city where God's temple is located.
God would dwell forever with the people in Jerusalem if they'd just stop oppressing the widow and the orphan and the alien, and stop shedding innocent blood and worshipping other gods. Is that too much to ask?
The people are abusing God's temple, claiming it as a sanctuary when they're really polluting it with all sorts of sins: adultery, Baal-worship, stealing, murder, and false oaths.
God tells the people to think about what happened to Shiloh in northern Israel: God checked out and the people were conquered and exiled.
He'll do the same thing to Jerusalem and treat them the same way he treated the northern Kingdom, so remember and learn.
God instructs Jeremiah and any righteous people not to pray for mercy for Jerusalem. The people keep going about their sinful ways: they pour drinks to offer to other gods and bake cakes to offer to the "queen of heaven." It's definitely wrath time.
God says people might as well go ahead and eat up their burnt offerings, because he never demanded sacrifices from them when he brought them out of Egypt. He just wanted obedience—love and justice and morality.
But instead, the people looked back to the way that they'd behaved in Egypt.
God tells Jeremiah that the people are so corrupt that they simply won't listen to the message he's bringing them.
Jeremiah is to tell them that they've been cut off from God: symbolically, they should cut their hair from their heads and wail in lamentation. God has forsaken them.
The people have brought foreign gods into God's own temple, and they've built an altar at Topheth to sacrifice their own children in fire—something God clearly didn't want.
That's the last straw. Judah will be a wasteland when God gets done with it.