"'A lion has come out of his lair; a destroyer of nations has set out. He has left his place to lay waste your land. Your towns will lie in ruins without inhabitant. So put on sackcloth, lament and wail, for the fierce anger of the Lord has not turned away from us.'" NIV translation
The prophet informs the people of Judah of the fact that their judgment has already been prepared as Babylon has already left their own land.
"'"In that day," declares the Lord, "the king and the officials will lose heart, the priests will be horrified, and the prophets will be appalled."'" NIV translation
The leaders of Judah will not be able to do anything in the face of the Babylonians. The priests and prophets will still be stuck in their self-righteous religion. The same thing is going to happen in the last days as Jesus warned in Matthew 7:22. Then, there will be prophets that Jesus tells that He did not even know them.
"Then I said, 'Alas, Sovereign Lord! How completely you have deceived this people and Jerusalem by saying, "You will have peace," when the sword is at our throats!'" NIV translation
Jeremiah acknowledges the fact that God has allowed the people to be deceived by those who said that there was not going to be a judgment. The same thing is going to happen in the last days as the Anti-christ gets the world to agree to a worthless peace treaty. We might ask ourselves why God would allow this deception. We just have to accept the fact that god knows the hearts of all men and He knows what He is doing.
"At that time this people and Jerusalem will be told, 'A scorching wind from the barren heights in the desert blows toward my people, but not to winnow or cleanse; a wind too strong for that comes from me. Now I pronounce my judgments against them.'" NIV translation
The coming judgment is compared to a wind and not the usual gentle breeze that separated the grain from the chaff. It is made perfectly clear that this judgment is going to fall upon all of the people. We should thank God that He deals with us on an individual basis and we do not get what we as a nation deserve.