What does Jeremiah 25:1 mean?

This message came to Jeremiah about all the people of Judah in the fourth year of Jehoiakim son of Josiah, king of Judah. That was the first year Nebuchadnezzar was king of Babylon. Jeremiah 25:1 - Modern Text Bible

(Jeremiah is setting the scene: this prophecy comes at a key moment, right as Babylon is rising to power.)