polooss umoough
polooss umoough voted up Anonymous' answer

Most likely his personal scribe, Baruch, actually put the words on paper or vellum.  In a time when nearly everyone was illiterate scribes did all the writing. Jeremiah dictated to his scribe the words of prophecy put into his heart by God. Not particularly surprising at all. 

polooss umoough
polooss umoough voted up Anonymous' answer

Most likely his personal scribe, Baruch, actually put the words on paper or vellum.  In a time when nearly everyone was illiterate scribes did all the writing. Jeremiah dictated to his scribe the words of prophecy put into his heart by God. Not particularly surprising at all.