19 Therefore thus saith the LORD, If thou return, then will I bring thee again, and thou shalt stand before me: and if thou take forth the precious from the vile, thou shalt be as my mouth: let them return unto thee; but return not thou unto them.
Consider to what a dignity one exalts himself who esteems others’ salvation to be of great importance. Such a person is imitating God as far as lies within the power of humankind. Hear what God says speaking through his prophet: “He who separates the worthy from the vile shall be as my mouth.” What God says is that one who is eager to save a brother who has fallen into careless ways, one who hastens to snatch his brother from the jaws of the devil, that person imitates me as far as lies within human power. What could equal that? This is greater than all good deeds. This is the peak of all virtue.
Let us catch them, then, by our mode of life; and by these souls let us build up the church, and of these let us amass our wealth. There is nothing to weigh against a soul, not even the whole world. Thus, although one may give countless treasure to the poor, in so doing he will not do such work as one who converts one soul. “For he who takes forth the precious from the vile shall be as my mouth,” so God speaks. A great good it is, I grant, to have pity on the poor, but it is nothing equal to removing them from error.
Words full of gentleness and meekness, even as Jesus also used to speak, saying to those who were insulting him, “I have not a devil,” and again, “If I have spoken wrongly, bear witness to the wrong.” If you also speak in this way, if you speak for your neighbor’s betterment, you will obtain a tongue like that tongue. And these things God says: “For he that brings out the precious from the vile shall be like my mouth”; such are his words.
It is obvious that the text above was said not by Jerusalem but by a prophet. To him the Lord responds, “If you turn from the sins of the people, I likewise will turn you from tribulation toward joyfulness, and you will stand before my face like the angels stand in the presence of God daily, beholding his face.” Also, if you separate the precious from the vile, you will become like my mouth. “Now should you think,” he adds, “that there is no reward for good works, if you distinguish my saints from the crowd of sinners in your speech, you will be as my mouth, and you will be united to my precepts. For sinners need to be imitators of you, not you of them. Nor should you fear and ask: ‘Why has my pain become perpetual and my wound worse (or incurable),’ such that I lose all hope of being healed? For I have made you like a bronze and impregnable wall, so that you can withstand all the strength of your adversaries. Moreover, you have me as a helper, and I will liberate you from the hand of the most evil (or pestilent), and I will redeem you with my blood (or with the presence of my help).” May we consider just how great a reward the speech of the teacher will have if it is able to liberate from error and to rescue from among the number of sinners!
(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 407] John Chrysostom on Jeremiah 15:19