Adam Clarke on Jeremiah 29:20

Hear ye therefore the word - Dr. Blayney thinks there were two letters written by the prophet to the captives in Babylon, and that the first ends with this verse. That having heard, on the return of the embassy (Elasah and Gemariah, whom Zedekiah had sent to Babylon, and to whom the prophet entrusted the above letter, Jer 29:3), that the captives had not received his advises favourably, because they were deceived by false prophets among them, who promised them a speedier deliverance, he therefore wrote a second letter, beginning with the fifteenth verse, and going on with the twenty-first, etc., in which he denounces God's judgments on three of the chief of those, Ahab, Zedekiah, and Shemaiah.