Charles Ellicott Commentary Jeremiah 36:9

"Now it came to pass in the fifth year of Jehoiakim the son of Josiah, king of Judah, in the ninth month, that all the people in Jerusalem, and all the people that came from the cities of Judah unto Jerusalem, proclaimed a fast before Jehovah." — Jeremiah 36:9 (ASV)

It came to pass in the fifth year of Jehoiakim. —The Septuagint gives “the eighth year,” but the Hebrew text gives the much more probable date.

What follows apparently refers to the same occasion as Jeremiah 36:8 and is of the nature of a note explaining the circumstances under which the prophetic discourse was read. An interval of some months thus passed between the writing of the book and its delivery in the Temple, during which its substance was, perhaps, made known to the inner circle of the prophet’s disciples. The fast was probably proclaimed when the king heard of the approach of Nebuchadnezzar’s army, as described by the Rechabites in Jeremiah 35:11.