What were the three major subjects about which Jeremiah wrote in the book by his name?

The major parts of the book of Jeremiah are usually delineated as follows: prophecies against Judah and Jerusalem (chapters 1-25), narratives about Jeremiah (chapters 26-45), prophecies against foreign nations (chapters 46-51), and a historical appendix (chapter 52). The prophecies in the first part of the book derive mostly from Jeremiah himself. The second part, which is mostly prose and usually speaks of Jeremiah in the third person, probably owes its composition to Baruch, the scribe who, according to chapter 36, wrote the prophecies against Israel and Judah and all the nations from Jeremiah’s dictation. The prophecies against foreign nations may derive in part from Jeremiah; the appendix was largely taken from 2 Kings 24:18-25:30.