John Gill Commentary Jeremiah 29:20

"Hear ye therefore the word of Jehovah, all ye of the captivity, whom I have sent away from Jerusalem to Babylon." — Jeremiah 29:20 (ASV)

Hear you therefore the word of the Lord
What he was now about to say concerning their false prophets: all you of the captivity, whom I have sent from Jerusalem to Babylon ;
all that were carried captive along with Jeconiah.

Some parts of this letter are directed to one sort of the captives, and others to another sort of them; some being good men, some bad; but what follows all are called upon to observe, good and bad; it being a prediction of a certain event, which they would see fulfilled in a short time; and therefore might be of service of them; to the godly, for the confirmation of them in the belief of what the Lord had promised; and to the rest, to make them stop giving heed to false prophets, that should hereafter arise.