15 Moreover if thy brother shall trespass against thee, go and tell him his fault between thee and him alone: if he shall hear thee, thou hast gained thy brother.
[AD 100] Didache on Matthew 18:15-17
And reprove one another, not in anger, but in peace, as you have it in the Gospel; [Matthew 18:15-17] but to every one that acts amiss against another, let no one speak, nor let him hear anything from you until he repents. But your prayers and alms and all your deeds so do, as you have it in the Gospel of our Lord.

[AD 253] Origen of Alexandria on Matthew 18:15-17
Let us look well whether this precept extends to all sin; for what if any one sin any of those sins which are unto death, such as unnatural crimes, adultery, homicide, or effeminacy, it cannot be meant that such as these are to be admonished privately, and if he hear you, forthwith to say that you have gained him. And not rather first put him out of the Church, or only when remaining obstinate after monition before witnesses, and by the Church? One man, looking at the infinite mercy of Christ, will say, that since the words of Christ make no distinction of sins, it is to go against Christ's mercy to limit His words only to little sins. Another, on the other hand, considering the words carefully, will aver, that they are not spoken of every sin; for that he that is guilty of those great sins is not a brother, but is called a brother, with whom, according to the Apostle, we ought not so much as to eat. But as they who expound this as referring to every sin give encouragement to the careless to sin; so, on the other hand, he, who teaches that one having sinned in little sins and such as are not deadly, is, when he has spurned the admonition of the witnesses and the Church, to be held as a heathen and a publican, seems to introduce too great severity. For whether he finally perishes, we are not able to decide. First, because he who has been thrice told of his fault and not hearkened, may hearken the fourth time; secondly, because sometimes a man does not receive according to his deeds, but beyond his trespass, which is good for him in this world; lastly, because He said not alone, Let him be as a heathen, but Let him be to thee. Whosoever then when reproved three times in a light trespass, does not amend, him we ought to hold for a heathen and a publican, avoiding him, that he may be brought to confusion. But whether he is esteemed of God also as a heathen and a publican, is not ours to decide, but is in the judgment of God.

[AD 407] John Chrysostom on Matthew 18:15
For, since He had used vehement language against them that cause offense, and on every hand had moved them to fear; in order that the offended might not in this way on the other hand become supine, neither supposing all to be cast upon others, should be led on to another vice, soften in themselves, and desiring to be humored in everything, and run upon the shoal of pride; do you see how He again checks them also, and commands the telling of the faults to be between the two alone, lest by the testimony of the many he should render his accusation heavier, and the other, become excited to opposition, should continue incorrigible.

Wherefore He says, Between you and him alone, and, If he shall hear you, you have gained your brother. What is, If he shall hear you? If he shall condemn himself, if he shall be persuaded that he has done wrong.

You have gained your brother. He did not say, You have a sufficient revenge, but, You have gained your brother, to show that there is a common loss from the enmity. For He said not, He has gained himself only, but, thou too hast gained him, whereby He showed that both the one and the other were losers before this, the one of his brother, the other of his own salvation.

This, when He sat on the mount also, He advised; at one time bringing him who has given the pain to him that had been pained, and saying, Be reconciled to your brother, and at another commanding him that had been wronged to forgive his neighbor. For He taught men to say, Forgive us our debts, like as we forgive our debtors. Matthew 6:12

But here He is devising another mode. For not him that gave the pain, does He now call upon, but him that was pained He brings to this one. For because this who has done the wrong would not easily come to make excuse, out of shame, and confusion of face, He draws that other to him, and not merely so, but in such way as also to correct what has been done. And He says not, Accuse, nor Charge him, nor Demand satisfaction, and an account, but, Tell him of his fault, says He. For he is held in a kind of stupor through anger and shame with which he is intoxicated; and thou, who art in health, must go your way to him that is ill, and make the tribunal private, and the remedy such as may be readily received. For to say, Tell him of his fault, is nothing else than Remind him of his error, tell him what you have suffered at his hand, which very thing, if it be done as it ought, is the part of one making excuse for him, and drawing him over earnestly to a reconciliation.
[AD 407] John Chrysostom on Matthew 18:15
He does not say “accuse him” or “punish him” or “take him to court.” He says “correct him.” For he is possessed, as it were, by some stupor, and drunk in his anger and disgrace. The one who is healthy must go to the one who is sick. You must conduct your judgment of him privately. Make your cure easy to accept. For the words “correct him” mean nothing other than help him see his indiscretion. Tell him what you have suffered from him.What then if he does not listen, if he stubbornly flares up? Call to your side someone else or even two others, so that two witnesses may corroborate all that’s said. For the more shameless and boldfaced he is, so much the more must you be earnest toward his cure, not toward satisfying your anger and hurt feelings. For when a physician sees the sickness unyielding, he does not stand aside or take it hard but then is all the more earnest. That then is what Christ orders us to do. You appeared too weak since you were alone, so become stronger with the help of others. Two are sufficient to reprove the wrongdoer. Do you see how he seeks the interest not of the aggrieved party alone but also that of the one who caused the grief? For the person injured may be the one who is more taken captive by passion. He becomes the one that is diseased and weak and infirm.
This effort may occur many times, as he attempts to lead him first alone and then with others. If he persists, then make the effort with the whole congregation. “Tell it,” he says, “to the church.” If he had sought the interest of the aggrieved alone, he would not have told him to approach the sick individual seventy-seven times. He would not have attempted so many times or brought so many treatments to the malady. He might have just let him be if he persisted uncorrected from the first meeting. But instead he shows us how to seek his cure once, twice, and many times: first alone, then with two, then with many more.

[AD 407] John Chrysostom on Matthew 18:15-17
(Hom. lx.) Having above given a severe sentence against those who were the cause of offence, making them to fear on all sides; so now that they to whom the offence is offered should not fall into the opposite fault of supineness and indifference, seeking to spare themselves in all things, and so be puffed up; the Lord here checks such a tendency, commanding that they be reproved, saying, If thy brother shall trespass against thee, go, tell him his fault between thee and him alone.

It is to be noted, that onewhile the Lord brings the offender to him whom he has offended; as when he says, If thou remember that thy brother has might against thee, go, be reconciled to thy brother: (Mat. 5:23.) otherwhiles He bids him that has suffered the wrong to forgive his neighbour; as where he says, Forgive us our debts, as we also forgive our debtors. (Mat. 6:12.) Here He has devised yet another method, for He brings him who has been grieved to him that grieved him, and therefore says, If thy brother sin against thee; for because he that did the wrong would not readily come to make amends, because of his shame, He draws to him him that has suffered the wrong; and not only draws him there, but with the very purpose of correcting what was done amiss; whence He says, Go and tell hint his fault.

And He says not, Accuse him, nor, Chide with him, nor, Demand redress,—but, Tell him of his fault; that is, remind him of his sin, tell him what things you have suffered from him. For he is held down by anger or by shame, stupefied as one in a deep slumber. Wherefore it behoves you who are in your right senses to go to him who is in a disease.

We are to tell his fault to the man himself who did it, and not to another, because the party takes it with the more patience from him, and above all when they are together alone. For when he who had a right to demand reparation, shows rather a carefulness to heal the sore, this has great power to propitiate.

In this it is made plain that enmities are a loss to both sides; for he said not, he has gained himself, but, you have gained him; which shows that both of you had suffered loss by your disagreement.

That is, to those that are over the Church.

Yet the Lord enjoins nothing of this sort to be observed towards those who are without the Church, such as He does in reproving a brother. Of those that are without He says. If any smite thee on the one cheek, offer to him the other also. (Mat. 5:39.) as Paul speaks, What have I to do to judge them that are without? (1 Cor. 5:12.) But brethren he bids us reprove, and turn away from.

[AD 420] Jerome on Matthew 18:15-17
What follows, Even so it is not the will, &c. is to be referred to what was said above, Take heed that ye despise not one of these little ones; and so He shows that this parable was set forth to enforce that same saying. Also in saying, It is not the will of my Father which is in heaven that one of these little ones should perish, He shows that so oft as one of these little ones does perish, it is not by the Father's will that it perishes.

If then your brother have sinned against you, or hurt you in any matter, you have power, indeed must needs forgive him, for we are charged to forgive our debtors their debts. But if a man sin against God, it is no longer in our decision. But we do all tho contrary of this; where God is wronged we are merciful, where the affront is to ourselves we prosecute the quarrel.

Thy brother is to be reproved in private, lest if once he has lost a sense of shame, he should continue in sin.

For in saving another, salvation is gained for ourselves also. Chrys What you should do if he does not yield is added, If he will not hear thee, take with thee one or two. For the more shameless and stubborn he shows himself, the more studious should we be of applying the medicine, and not turn to wrath and hate. As the physician, if he see that the disease does not abate, he does not slack, but redoubles his efforts to heal. And observe how this reproof is not for revenge, but for correction, seeing his command is not to take two with him at first, but when he would not amend; and even then he does not send a multitude to him, but one or two, alleging the law, That in the mouth of two or three witnesses every word may stand. (Deut. 19:15.) This is that you may have witnesses that you have done all your part.

Or it is to be understood in this way; If he will not hear thee, take with thee one brother only; if he yet will not hear, take a third, either from your zeal for his amendment, that shame or admonition may move him; or for the purpose of meeting before witnesses.

If yet he will not hear them, then it must be told to many, that he may be held in abhorrence; so that he who could not be saved by his own sense of shame, may be saved by public disgrace; whence it follows, If he will not hear them, tell it to the Church.

That He says, As a heathen and a publican, shows that he is to be more abhorred, who under the name of a believer does the deeds of an unbeliever, than those that are openly gentiles. Those He calls publicans, who pursue worldly gain, and levy contributions by trading, cheating, and villainous frauds, and perjuries.

[AD 420] Jerome on Matthew 18:15-17
(Verse 15 and following) But if your brother sins against you, go and confront him between you and him alone. If he listens to you, you have gained your brother. But if he does not listen, take one or two more with you, so that by the testimony of two or three witnesses every word may be confirmed. If he refuses to listen to them, tell it to the church. And if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector. If our brother sins against us, and he harms us in any way, we have the power, indeed the necessity, to forgive our debtors as is commanded. But if someone sins against God, it is not within our power. For divine Scripture says: If a man sins against another man, the priest will pray for him. But if someone sins against God, who will pray for him? On the contrary, we are kind in the face of God's injustice, and in our own insults we exercise hatred. However, the brother must be rebuked privately, so that if he has once lost shame and modesty, he may not remain in sin. And if indeed he listens, we gain his soul, and through the salvation of another, we also acquire salvation for ourselves. But if he refuses to listen, let a brother be called in. And if he does not listen to him, let a third person be called in, either to correct him or to meet with witnesses. But if he refuses to listen to them as well, then it is necessary to bring in many people, so that he may be held in detestation, and let him who could not be saved by shame be saved by disgrace. However, when it is said, 'Let him be to you as a Gentile and a tax collector,' it is shown that there is a greater detestation for someone who acts as a faithful person under the title of an infidel than for those who openly identify as Gentiles. For publicans are called according to tropology, those who pursue worldly gains and demand taxes through dealings and frauds, thefts, and wicked perjuries.

[AD 430] Augustine of Hippo on Matthew 18:15-17
(Serm. 82. 1.) Our Lord admonishes us not to overlook one another's faults, yet not so as seeking for matter of blame, but watching what you may amend. For our rebuke should be in love, not eager to wound, but anxious to amend. If you pass it by, you are become worse than he. He by doing you a wrong hath done himself a great hurt; you slight your brother's wound, and are more to blame for your silence than he for his ill words to you.

(de Civ. Dei, i. 9.) For often we wrongly shun to teach and admonish, or to rebuke and check the wicked, either because the task is irksome, or because we would escape their enmity, lest they should harm or obstruct us in temporal things, whether in gaining objects we desire, or in holding what our frailty fears to love. But if any one spares reproof of evil doers, because he seeks fitter occasion, or fears to make them worse, or that they may be an impediment to the good and pious living of other weak ones, or may grieve them, or turn them from the faith; herein there is seen no considerations of covetousness, but the prudence of charity. And much weightier reason have they who are set over the churches, to the end they should not spare to rebuke sin; though not even he is free from this blame, who, though not in authority, wots of many things in them to whom he is bound by the ties of this life, which should be touched by admonition or correction, but neglects to do so; shunning their displeasure on account of things which he does not unduly use in this life, but wherewith he is unduly delighted.

(Serm. 82, 7.) When any one therefore offends against us, let us be very careful, not for ourselves, for it is glorious to forget an injury; forget therefore your own wrong, but not the wound your brother has sustained; and tell him of his fault between him and you alone, seeking his amendment and sparing his shame. For it may be that out of shame he will seek to defend his fault, and thus you will only harden, while you sought to do him good.

(ubi sup.) But the Apostle says, Them that sin 'rebuke before all, that others may fear to do the like. (1 Tim 5:20.) Sometimes therefore your brother is to be spoken to between thee and him alone, sometimes to be rebuked before all. What you must do first, attend and learn; If thy brother, says He, sin against thee, tell him of his fault between thee and him alone. Why? Because he has sinned against you? What is it that he has sinned against you? You know that he has sinned, and therefore since his sin was in private, let your rebuke be in private too. For if you alone know of his trespass, and proceed to rebuke him before all, you do not correct but betray him. Your brother has sinned against you; if you alone know thereof, then he has sinned against you only; but if he did you a wrong in the presence of many, then he has sinned against those also who were witnesses of his fault. Those faults then are to be rebuked before all, that are committed before all; those which are done in private, are to be rebuked in private. Discern times, and the Scriptures are consistent. But why do you correct your neighbour? Because his trespass has hurt yourself? Far be it from thee. If you do it from self-love, you do nought; if you do it from love of him, you do most rightly. Lastly, in what you shall say to him, keep in view for whose sake it is that you ought to do it, for your own or for his, for it follows, If he hear thee, thou hast gained thy brother; do it therefore for his sake, that you may gain him. And do you confess that by your sin against man you were lost; for if you were not lost, how has he gained you? Let none then make light of it when he sins against his brother.

(Serm. 82, 7.) That is, regard him no longer in the number of thy brethren. Though even thus we are not to neglect his salvation; for the heathens themselves, that is, the gentiles and pagans, we do not indeed regard in the number of our brethren, yet we ever seek their salvation.

[AD 500] Desert Fathers on Matthew 18:15
A brother learnt that another brother was angry with him, and went to make it up but the other did not open the door of his cell. So he went to a hermit, and told him about it. The hermit said, ‘See that you have no reason, which looks like a just reason, in your heart for blaming your brother: as though you would accuse him and justify yourself, for if so God will not touch his heart to open the door to you. I tell you this: even if he has sinned against you, think in your heart that you have sinned against him; justify your brother rather than yourself and then God will put it into his heart to make peace with you.’

[AD 856] Rabanus Maurus on Matthew 18:15-17
He does not command us to forgive indiscriminately, but him only that will hearken and be obedient, and do penitence; that neither should forgiveness be unattainable, nor sufferance be too far relaxed.

[AD 1274] Glossa Ordinaria on Matthew 18:15-17
(ap. Anselm.) Or, that if he affirm that it is no trespass, that they may prove to him that it is a trespass.

(ap. Anselm.) Or, tell it to the whole Church, that his infamy may be the greater. After all these things follows excommunication, which ought to be inflicted by the mouth of the Church, that is, by the Priest, and when he excommunicates, the whole Church works with him; as it follows, And if he will not hear the Church, let him by unto thee as an heathen, and a publican.