18 Verily I say unto you, Whatsoever ye shall bind on earth shall be bound in heaven: and whatsoever ye shall loose on earth shall be loosed in heaven.
[AD 253] Origen of Alexandria on Matthew 18:18-20
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.

He said not in the heavens (in cœlis), as when He spoke to Peter, but in heaven (in cœlo), for they are not yet attained to the like perfection with Peter.

And He said not, I will be, but I am in the midst of them; because straightway, as soon as they have agreed together, Christ is found among them.

And this also is the reason why our prayers are not granted, because we do not agree together in all things upon earth, neither in doctrine, nor in conversation. For as in music, unless the voices are in time there is no pleasure to the hearer, so in the Church, unless they are united God is not. pleased therein, nor does He hear their words.

Or, In whatever the two testaments are in agreement, for this every prayer is found acceptable to God.

[AD 253] Origen of Alexandria on Matthew 18:18
After stating that the one judged is viewed as a heathen and tax collector, something else is added which is well put: “Truly, I say to you”—clearly to those judging someone to be as a heathen and tax collector—“whatever you bind on earth shall be bound in heaven.” For he who has three times admonished him and not been heard has justly bound him, and that man is then to be thought judged as a heathen and tax collector. Therefore when a man like this has been bound and condemned by someone, he remains bound insofar as none of those in heaven rescinds the judgment of the man by whom he was bound. So too the man who has once been warned and does things worthy of being won back is released through the warning of the one who wins him back. He is no longer bound by the bonds of his sins for which he was warned and bound; he will be judged by those in heaven as set free.

[AD 367] Hilary of Poitiers on Matthew 18:18-20
To hold out a great and terrible fear, by which all men should be reached in this present life, He pronounces that the judgment of the Apostles should be ratified, so that whosoever they bound on earth, i. e. left entangled in the noose of sin, and whosoever they loosed, i. e. accorded the pardon of God's mercy to their salvation, that these should be bound and loosed in heaven.

For He who is peace and charity, will set His place and habitation in good and peaceable dispositions.

[AD 407] John Chrysostom on Matthew 18:18-20
And be it noted, that He said not to the Primate1 of the Church, Bind such a man; but, If ye shall bind him, the bonds shall be indissoluble; leaving the other to his discretion. And see how He has set the incorrigible person under the yoke of a twofold necessity; to wit, the punishment that is here, namely, the casting forth out of the Church, when He said, Let him be to thee as a heathen; and the future punishment, saying, that he shall be bound in heaven; thus by the weight of his penalties lessening his brother's wrath against him.

Or, because He had said, It shall be done unto them by My Father; therefore, to show that He is the Giver together with His Father, He adds this, where two or three, &c.

Yet He said not barely, Where they are gathered together, but added, in my name, as much as to say, If any man look upon Me as the chief motive of his love to his neighbour, I will be with him, though he is virtue be shown towards other men. How is it then that those who thus agree together do not obtain what they ask for? First, because they ask things not expedient, and because they do not bring on their parts that which they ought to contribute; wherefore He says, If two of you, that is, who show an evangelic conversation. Thirdly, because they pray seeking vengeance against those who have grieved them. And fourthly, because they seek mercy for sinners who have not repented.

[AD 407] John Chrysostom on Matthew 18:18
He did not say to the leader of the church, “bind him” but “if you bind him,” leaving the whole entire decision to the one aggrieved. Only after a due process do the bonds remain unbreakable, and so he will suffer the worst fate. It is not the one who has called for accountability that is to blame but the one who had not been willing to be persuaded. Do you see how Christ has bound him with a twofold constraint, both by the chastisement here and by the punishment hereafter? He threatens the one punishment to prevent the other from happening. Thus, by fearing both rejection from the church and the threat of being bound in heaven, he may become better behaved. And knowing these things, if not at the beginning, at any rate through so many judgments he will put off his anger. For this reason, Jesus set up a first and a second and a third judging. He does not immediately cut him down, so that if he does not obey the first, he may still yield to the second. But if he rejects that too, he may still respect the third. But if he takes no account of this third danger, let him be terrified of future punishment, of God’s sentence and vengeance.

[AD 407] John Chrysostom on Matthew 18:18
But why did He set him with these? To soothe the person wronged, and to alarm him. Is this only then the punishment? Nay, but hear also what follows. Whatsoever you shall bind on earth shall be bound in Heaven. And He did not say to the ruler of the church, Bind such a man, but, If you bind, committing the whole matter to the person himself, who is aggrieved, and the bonds abide indissoluble. Therefore he will suffer the utmost ills; but not he who has brought him to account is to blame, but he who has not been willing to be persuaded.

Do you see how He has bound him down with twofold constraint, both by the vengeance here, and by the punishment hereafter? But these things has He threatened, that these circumstances may not arise, but that fearing, at once the being cast out of the church, and the danger from the bond, and the being bound in Heaven, he may become more gentle. And knowing these things, if not at the beginning, at any rate in the multitude of the tribunals he will put off his anger. Wherefore, I tell you, He has set over him a first, and a second, and a third court, so that though he should neglect to hear the first, he may yield to the second; and even if he should reject that, he may fear the third; and though he should make no account of this, he may be dismayed at the vengeance to come, and at the sentence and judgment to proceed from God.
[AD 420] Jerome on Matthew 18:18-20
Because He had said, If he will not hear the Church, let him be to thee as a heathen, and a publican, whereupon the brother so contemned might answer, or think within himself, If you despise me, I also will despise you; if you condemn me, you shall be condemned by my sentence. He therefore confers powers upon the Apostles, that they may be assured that when any are condemned after this manner, the sentence of man is ratified by the sentence of God. Verily I say unto you, Whatsoever ye shall bind on earth shall be bound in heaven; and whatsoever ye shall loose upon the earth shall be loosed in heaven.

Or otherwise; All His foregoing discourse had invited us to union; now to make us embrace peace more anxiously, He holds out a reward, promising to be in the midst of two or three.

(vid. Origen. in loc.) We may also understand this spiritually; where our spirit, soul, and body are in agreement, and have not within them conflicting wills, they shall obtain from My Father every thing they shall ask; for none can doubt that that demand is good, where the body wills the same thing as the spirit.

[AD 420] Jerome on Matthew 18:18
(Verse 18.) Truly I tell you: whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven. For it was said: If, however, he does not listen to the Church, let him be to you like a Gentile and a tax collector, and it could be a hidden response of contempt for a brother, or a silent thought, if you despise me, I despise you, if you condemn me, you will be condemned by my judgment: he gives the power to the apostles, so that they may know that those who are condemned by such are confirmed by human judgment, and whatever is bound on earth is bound equally in heaven.

[AD 428] Theodore of Mopsuestia on Matthew 18:18
Well introduced were the words “whatever you loose,” since he shows that if they loose those who repent, their action has power, since the church in heaven and on earth is one. Anyone who does not want to be loosed from the bond of his sin but draws it to himself by the alienation of the saints is alienated also from the church in heaven and accordingly is also bound by it. Hence, if one is earnest about being loosed and receives the loosing of the saints when they “ratify their love for him,” as Paul teaches, he will belong in the heavenly church and be loosed from the bondage of the judgment.

[AD 430] Augustine of Hippo on Matthew 18:18-20
(ubi sup.) Otherwise; When you begin to hold your brother as a publican you bind him on earth, but take heed that you bind him with just cause; for an unjust cause breaks rightful bonds. But when you have corrected him, and agreed with him, you have loosed him upon earth, and when you have loosed him upon earth, he shall be loosed also in heaven. You confer a great boon not on yourself, but on him, as he had done the hurt not to you but to himself.

[AD 430] Augustine of Hippo on Matthew 18:18
This then is what we have heard the Lord advising, and with such great particularity that he himself adds, “Truly, I say to you, whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.” So the very moment you begin to hold your brother as an outsider to the covenant community, “you bind him on earth.” But see to it that you bind him justly. For unjust bonds will by justice soon be burst apart.… When you have admonished him and have been “reconciled to your brother,” you have thereby “loosed him on earth.” And when “you shall have loosed him on earth, he shall be loosed in heaven” also. So this is a weighty matter. You do this not for yourself but for him. For the harm he has done is not primarily to you but to himself.

[AD 1107] Theophylact of Ohrid on Matthew 18:18
. If you, He says, who have been wronged deem the wrongdoer a publican and a Gentile, he shall be so in heaven as well. And if you loose, that is, forgive him, he shall be forgiven in heaven as well. For it is not only what the priests loose that is loosed, but also whatever we who have been wronged bind or loose, those things too shall be either bound or loosed.
[AD 1274] Glossa Ordinaria on Matthew 18:18-20
(ap. Anselm.) But He holds out a ratification not only of sentences of excommunication, but of every petition which is offered by men holding together in the unity of the Church; for He adds, Again I say unto you, that if two of you shall agree upon earth, whether in admitting a penitent, or casting out a forward person, touching any thing which they shall ask, any thing, that is, that is not against the unity of the Church, it shall be done for them by my Father which is in heaven. By saying, which is in heaven, He points Him out as above all, and therefore able to fulfil all that shall be asked of Him. Or, He is in the heavens, that is, with saints, proof enough that whatever worthy thing they shall ask shall be done unto them, because they have with them Him of whom they ask. For this cause is the sentence of those that agree together ratified, because God dwells in them, For where two or three are gathered together in my name, there am I in the midst of them.