Charles Ellicott Commentary Jeremiah 15:20

"And I will make thee unto this people a fortified brazen wall; and they shall fight against thee, but they shall not prevail against thee; for I am with thee to save thee and to deliver thee, saith Jehovah." — Jeremiah 15:20 (ASV)

I will make thee unto this people ... —It is significant that the promise reproduced the very words which the prophet had heard when he was first summoned to his work (see Note on Jeremiah 1:18-19). Jehovah had not been unfaithful to His word, but, like all promises, it depended on implied conditions, and these the faint-hearted, desponding prophet had but imperfectly fulfilled. Let him “return” to the temper of trust, and there should be an abundant deliverance for him.