John Gill Commentary Jeremiah 51:60

"And Jeremiah wrote in a book all the evil that should come upon Babylon, even all these words that are written concerning Babylon." — Jeremiah 51:60 (ASV)

So Jeremiah wrote in a book all the evil that should come upon Babylon The evil of punishment predicted and threatened: this he delivered, not by word of mouth to Seraiah to relate when he came to Babylon; but he wrote it in a book for him reread; and he wrote it himself; Baruch, his amanuensis, not being now with him: [even] all these words that are written against Babylon ; in this and the preceding chapter: this book written by Jeremiah was a copy of them.