Jeremiah 36:4 - Joseph Benson’s Commentary on the Old and New Testaments

Then Jeremiah called Baruch Baruch was the most faithful disciple of this prophet: he served him as long as he lived in the capacity of his secretary, and never left him till his death. And Baruch wrote from the mouth of Jeremiah all the words, &c. We need not ask how Jeremiah could remember all the prophecies that he had prophesied, for twenty-two years before, considering who it was that commanded him to put them in writing. God undoubtedly brought them to his remembrance, otherwise it would have been impossible for him to have recollected them all. The Spirit of God dictated to Jeremiah, and he to Baruch.