Hashem tells Yirmiyahu B"Y must stop doing Avoda Zara and be kind to one another. He reminds Yirmiyahu of Shiloh, and proves that He can destroy the Beit HaMikdash again. Hashem repeats "Heichal Hashem" 3x because, as Radak explains, for the 3 sections of the Beit HaMikdash.
Hashem tells Yirmiyahu that he shouldn't daven for B"Y. Hashem explains how Avoda Zara a family affair and He doesn't want their Karbanot. Hashem also says that although now He is taking away the joy and happiness of weddings, it will be back one day.
Yirmiyahu goes to B"Y and tells them about his prophecy from Hashem. He warns them to change their ways, or else Hashem will send nations to destroy them and the Beit HaMikdash.
Good, Hashem wouldn't have been happy if you had killed me.
He shall live!
B"Y go to the town officials after hearing Yirmiyahu's prophecy and tell them he must be put to death. They say how he was lying and speaking against the land and must be killed.
The officials recall the previous Navis who gave similar Nevuahs to B"Y. One of them, Micah (left), was allowed to live and B"Y fixed their ways. The other one, Uriyah (right), was killed for what he said. It seems a little confusing that the officials brought Uriyah up, so Rashi explains that this is actually a new speaker from the ppl who want to kill Yirmiyahu.
In the end, the officials all agree that Yirmiyahu will live and Yirmiyahu is saved.