Albert Barnes Commentary Jeremiah 30:2

"Thus speaketh Jehovah, the God of Israel, saying, Write thee all the words that I have spoken unto thee in a book." — Jeremiah 30:2 (ASV)

Write ... in a book - To be read and meditated upon by them in private. This makes it exceedingly probable that the date of these two chapters was also the 10th year of Zedekiah, immediately after the purchase of the field from Hanameel.

All the words - that is, the scroll was to be a summary of whatever hope and mercy had been contained in previous predictions.