20 And I will make thee unto this people a fenced brasen 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 the LORD.
(Verse 19 onwards) Because of this, the Lord says: If you turn back, I will restore you, and you shall stand before me. And if you separate the precious from the vile, you shall be like my mouth. They will turn to you, but you shall not turn to them. And I will make you to this people a fortified bronze wall; and they will fight against you, but they shall not prevail, for I am with you to save you and deliver you, says the Lord. And I will deliver you from the hand of the wicked, and redeem you from the hand of the strong (or the pestilent). It is clear that the things mentioned do not pertain to Jerusalem, but rather the Prophet said them. To whom the Lord responded, if you turn the people away from sins, I will turn you from tribulation to joy, and you will stand before my face, just as the Angels stand in the presence of God, seeing His face daily. And if you separate the precious from the vile, you will be like my mouth. Do not think, he says, that there is no reward for good works: if you separate even my saints from the number of sinners with your words, you will be like my mouth, and you will be connected to my commandments. For indeed they should be your imitators, and not you theirs. Do not be dismayed, and say: Why has my pain become perpetual, and my wound strong or hopeless, so that I despair of being able to be healed. For I will give you like a wall of bronze, strongest, so that you may resist the adversary with all strength; and you will have me as a helper and I will free you from the hand of the wicked or the pestilence, and I will redeem you, either with my own blood or for now with my help. Let us consider what reward the teaching of a doctor has, if he is able to free someone from error and lead them out of the number of sinners.
[AD 420] Jerome on Jeremiah 15:19-21