Even though Jeremiah knows that God's in the right, he says that he personally wants to air some grievances.
He asks why the wicked have been doing so well without being punished.
He asks God to kill the wicked and relieve the people's suffering.
God answers that if Jeremiah is tired from dealing with these wicked people, he's like someone who has been exhausted from racing with foot-runners. So how can he compete when racing with horses (i.e. with really wicked opponents)?
Jeremiah shouldn't even trust his own family.
God says that he's forsaken Israel, even though they're still totally his favorite people.
But since the people of Israel apparently hate God now, he's leaving them to the wild animals.
Evil shepherds (metaphorically speaking) have trampled down the vineyard that God had planted in Judah and Jerusalem. They've ruined the land.
God isn't just going to punish Judah, but all the neighbors who've led them astray.
Then God will have compassion on the people of these different neighboring nations and Judah, and will let them return.
If they can worship God as they used to worship Baal, he'll have mercy on them. But if they don't, he'll tear them up and throw them out.