Matthew Poole and continuators on Jeremiah 21:9

9 He that abideth in this city, shall die by the sword, and by the famine, and by the pestilence: but he that goeth out, and falleth to the Chaldeans that besiege you, he shall live , and his life shall be unto him for a prey .

But certainly if ever any man spake High Treason, this Prophet now did it, when there was an Enemy besieging them, telling them, that if they would save their lives, they must Revolt from their King, and join with their Enemies, all that can be said in excuse for the Prophet is, that this was a Divine Revelation to him, and a Message sent to the King himself.

His life shall be given him for a prey appeareth to have been a proverbial Expression, either signifying a mans Possession of his life, as a prey, or booty recovered from death, or the hand of the Enemy. 2. Or a mans rejoycing in the saving of his life, as if he had got some notable booty.

Marginal references: chap. 38.2:; chap. 39.18. & 45.5.