What does Jeremiah 29:1 mean?

These are the words of the letter that Jeremiah the prophet sent from Jerusalem to the elders who were still alive among the exiles, to the priests, the prophets, and all the people Nebuchadnezzar had taken from Jerusalem to Babylon. Jeremiah 29:1 - Modern Text Bible

(Jeremiah writes a letter to the Jewish leaders and people who have been exiled to Babylon, addressing their new reality.)