Albert Barnes Commentary Jeremiah 36:2

"Take thee a roll of a book, and write therein all the words that I have spoken unto thee against Israel, and against Judah, and against all the nations, from the day I spake unto thee, from the days of Josiah, even unto this day." — Jeremiah 36:2 (ASV)

A roll of a book - A parchment scroll, consisting of several skins sewn together, and cut to an even width, with a piece of wood at one end (or, in case of larger volumes, at both ends) on which to roll them up.

Write therein all the words ... - The phrase means that the roll was to contain all the counsel of God (Acts 20:27) on the special point mentioned in Jeremiah 36:3; and that the prophet was not to keep anything back.