Matthew 6:14,15 (Luther)

MATTHEW 6:14. For if you forgive men their trespasses, your heavenly Father also will forgive you; 15. But if you do not forgive men their trespasses, neither will your Father forgive your trespasses.

This is a remarkable addition, but a very precious one. Someone may well wonder why He should append this addition to this particular petition: “Forgive us our debts.” He could just as well have appended some such item to one of the others, and He could have said: “Give us our daily bread, as we give it to our children”; or, “Lead us not into temptation, as we do not tempt anyone”; or, “Deliver us from evil, as we save and deliver our neighbors.” Yet the only petition that has an addition of this sort is this one, and it gives the impression that the forgiveness of sins is accomplished and merited by our forgiving. Then what would become of our doctrine that forgiveness must come only through Christ and must be received in faith?
The answer to the first part of the question is this: by putting the petition this way and connecting the forgiveness of sin with our forgiving, He had the special purpose of making mutual love a Christian obligation, and the continual forgiveness of the neighbor the primary and foremost duty of Christians, second only to faith and the reception of forgiveness. As we live in faith toward Him, therefore, so also we should live in love toward our neighbor. We should not bring annoyance or injury upon one another, but keep in mind always to forgive one another even though we have been injured, as is inevitable in this life; we should know that otherwise we shall not be forgiven either. Where anger and ill will are an obstacle, this spoils the whole prayer and prevents one from being able to pray or to wish any of the preceding petitions either. You see, this means we must establish a firm and strong bond that will hold us together. When we plan to come before God in prayer for what we are to obtain, we must not be disunited or divided into schisms, factions, and sects, but we must be tolerant toward one another in love and remain of one mind. When this is the case, the Christian man is perfect; he believes correctly, and he loves correctly. Whatever other faults he may have, these are to be consumed in his prayer, and it is all forgiven and remitted.
But how is it that by these words He establishes such a close connection between forgiveness and our works when He says: “If you forgive your neighbor, you will be forgiven,” and vice versa? That does not seem to make forgiveness dependent upon faith. Answer: As I have often said elsewhere, the forgiveness of sins takes place in two ways: first inwardly, through the Gospel and the Word of God, which is received by faith in the heart toward God; second, outwardly through works, about which 2 Peter 1:10 says in its instructions regarding good works: “Dear brethren, be zealous to confirm your calling and election.” He means to say that we should confirm our possession of faith and the forgiveness of sin by showing our works, making the tree manifest by means of its fruit and making it evident that this is a sound tree and not a bad one (Matt. 7:17). Where there is a genuine faith, there good works will certainly follow, too. In this way a man is pious and upright, both inwardly and outwardly, both before God and before men. For this follows as the fruit by which I assure myself and others that I have a genuine faith; this is the only way I can know or see this.
In this passage, similarly, the outward forgiveness that I show in my deeds is a sure sign that I have the forgiveness of sin in the sight of God. On the other hand, if I do not show this in my relations with my neighbor, I have a sure sign that I do not have the forgiveness of sin in the sight of God but am still stuck in my unbelief. You see, this is the twofold forgiveness: one inward in the heart, clinging only to the Word of God; and one outward, breaking forth and assuring us that we have the inward one. This is how we distinguish works as outward righteousness from faith as inward righteousness, but in such a way that the inward has precedence as the stem and root from which the good works must grow as fruit. Outward righteousness, however, is the witness of this, and as Peter says, its “certification,” an assurance that the other is really present. Whoever lacks the inward righteousness does not do any of the outward works. On the other hand, where the outward signs and proofs are lacking, I cannot be sure of the inward, but I am deceiving both myself and others. But if I look and find myself gladly forgiving my neighbor, then I can draw this conclusion and say: “I am not doing this work naturally, but by the grace of God I feel different from the way I used to be.”
Let this brief answer suffice against the idle talk of the sophists. But it is also true that this work, as He discusses it here, is not a mere work like the others, which we do of ourselves; for it does not ignore faith. He takes the work and puts a promise on top of it, so that it might quite appropriately be called a sacrament, a means of strengthening faith. For example, Baptism, too, should be regarded as a work that I do when I baptize or am baptized. But since the word of God is present in it, it is not a mere work that amounts to something or accomplishes something of itself, but a divine word and sign upon which faith depends. In the same way, our prayers as our own work would not amount to anything or accomplish anything; but what makes it amount to something is the fact that it proceeds on the basis of His commandment and promise. For that reason it may well be regarded as a sacrament and as a divine work rather than a work ofour own.
The reason I say this is that the sophists pay attention to the works we do on our own, apart from the word and promise of God. Therefore, when they hear and read statements like these, making mention of works, they have to say that man merits this by his action. But the Scriptures teach us otherwise. We should not look to ourselves but to the word and promise of God, clinging to it by faith. Then if you do a work on the basis of this word and promise, you have a sure indication that God is gracious to you. In this way your own work, which God has now taken to Himself, is to be a sure sign of forgiveness for you.
Now God has provided us with various means, ways, and channels, through which to take hold of grace and the forgiveness of sin: first, Baptism and the Sacrament; also, as I have just said, prayer; also absolution; and our forgiveness throughout. Thus we are abundantly taken care of, and we can find grace and mercy everywhere. Where would you look for it any closer than with your neighbor, with whom you live every day and toward whom every day you have ample reason to practice this forgiveness? It is inevitable that you should be offended, deeply and often. It is, therefore, not only in the church or in the presence of the priest, but in the very midst of our own life, that we have a daily sacrament or baptism, one brother with another and everyone at home in his house. For if you take hold of the promise through this work, you have the very thing that you receive in Baptism. How could God have endowed us more richly with His grace than by hanging such a common baptism around our necks and attaching it to the Lord’s Prayer, a baptism that everyone discovers in himself when he prays and forgives his neighbor? Now, no one has any reason to complain or to make the excuse that he cannot get around to it, or that it is too sublime and distant for him, or that it is too difficult and expensive; for it has been brought home to him and his neighbor and planted on his very doorstep, in fact, put into his very bosom.
So you see that if you look at it not on the basis of the work itself but on the basis of the word that is attached to it, you find in it a wonderful and precious treasure. Now it is no longer your work, but a divine sacrament and a great and powerful comfort that you can attain to the grace of being able to forgive your neighbor, even though you may not be able to come to the other sacraments. This should prompt you to do this work gladly and from the heart and to thank God that you are worthy of such grace. You ought to pursue this even to the end of the world and spend everything you have for it, as we used to do for those fake indulgences. Whoever refuses to accept this must really be a shameful and accursed man, especially if he hears and acknowledges this grace and still remains so bent and stubborn that he refuses to forgive. By such a refusal he simultaneously loses both Baptism and the Sacrament, along with everything else. For they are all linked together, and whoever has one should have them all or keep none of them. Whoever is baptized should also receive the Sacrament; whoever receives the Sacrament must also pray; and whoever prays must also forgive. If you do not forgive, you have a terrible sentence here: your sins will not be forgiven either, even though you are in a Christian company and are enjoying the Sacrament and other benefits; in fact, your sins will damage and damn you all the more on account of this.
In order to arouse us even further in file direction of doing this, Christ has used kind and friendly words, saying, “If you forgive men their trespasses,” rather than saying “their malice and wickedness” or “their insolence and viciousness.” He uses “trespass” to designate the kind of sin that is committed more from weakness or ignorance than from malice. Now, why should He minimize and underemphasize the sin of our neighbor this way? After all, we often see many people sinning deliberately, out of sheer viciousness and a malicious will. He does it in order to put your anger to rest and to soften you so that you are glad to forgive. He is more interested in making your heart sweet and friendly than in making the sin as great as it really is in itself. For in the sight of God it is and should be great enough to be worthy of eternal damnation and to lock the gates of heaven, even though it is only a tiny sin or a failing, as long as the sinner does not confess it and beg your pardon for it.
But He does not want you and me to look at the sin this way. It is not up to us to punish the sin but to forgive it. This is the way you ought to think: although your neighbor has acted against you out of malice,8 still he is confused, captivated, and dazzled by the devil. Therefore you should be pious enough to take pity on him for being overpowered by the devil. As far as the devil is concerned, then, this may be called a great and unforgivable sin, since he has put the man up to it. But as far as the man himself is concerned, it should be called a trespass and a fault. This is what Christ Himself has done toward us by praying on the cross (Luke 23:34): “Father, forgive them; for they know not what they do.” That minimized our sin and underemphasized it, though in itself it was the very greatest sin that had ever taken place on earth. For what greater sin can there be than this shameful torture and murder of God’s only Son?
Yet you must treat this mistake and fault in such a way that the neighbor who has sinned against you confesses it, asks for forgiveness, and decides to improve. Elsewhere9 I have said that there are two kinds of sin: one kind is confessed, and this no one should leave unforgiven; the other kind is defended, and this no one can forgive, for it refuses either to be counted as sin or to accept forgiveness. When Christ talks about forgiveness or the keys in Matthew 18:18, therefore, He puts the two side by side, loosing and binding, to make this clear. It is impossible to loose a sin which a person refuses to acknowledge as a sin that needs to be forgiven; such a sin should be bound to the abyss of hell. On the other hand, those sins that are confessed should be loosed and elevated to heaven. This provision in the Office of the Keys also applies to the relation of every Christian with his neighbor. He should be ready to forgive everyone that injures him. And yet, if someone refuses to acknowledge the sin and to stop it, but persists in it, you cannot forgive him—not on your account but on his, because he refuses to accept the forgiveness. But as soon as he owns up to being guilty and requests forgiveness, everything must be granted, and the absolution must follow right away. Since he is punishing himself and desisting from his sin, so that there is no longer any sin about him, I should let the matter of his sin drop. But if he holds on to it and refuses to drop it, I cannot take it from him but must let him remain stuck in it; for he himself has changed a forgivable sin into an unforgivable one. In other words, if he refuses to confess, his conscience must be burdened as heavily as possible, without any sign of grace; for he stubbornly insists upon being the devil’s own. On the other hand, if he confesses his sin and begs your pardon but you refuse to forgive him, you have loaded the sin upon yourself, and it will condemn you as well.
By referring to a sin as a “trespass,” therefore, Christ means that it should be confessed; He does not mean to deny that it is wrong. Nor is He making it your duty to approve of it as if it were the right kind of behavior. Rather, you should treat it as right or good only on the condition that it has become forgivable, so tiny as to be called only a fault. Then you can say to your neighbor: “I cannot approve of it, and it is still wrong. Nevertheless, because you make your confession and because your heart is different now and you have no resentment against me, I will gladly make the concession of calling it a fault and an oversight, and I will refrain from any anger.”
Now, if you take this attitude toward your neighbor, God will likewise treat you with that kind of sweet and friendly heart. That great and grave sin that you have committed against Him and are still committing, He will make so tiny that He will call it only a fault if you confess it and ask for forgiveness; for He is more inclined to forgive than we can imagine Him to be. To bribe God into having this kind of heart toward you, you would certainly be willing to surrender your body and life and to travel to the end of the world, the way people used to travel in the days of the papacy, torturing themselves for it with many kinds of works. But now such a heart is being offered to you here, presented and granted completely free, as are Baptism, the Gospel, and all His blessings. You receive more than you could ever acquire with all your works and the works of all men combined. Here you have a sure promise, one that neither deludes nor deceives you, that, however many or great all your sins may be, in His sight they are to be as tiny as mere everyday human weaknesses, which He will not count or remember as long as you have faith in Christ. Other Sacraments have their source and their power in Christ, the Lord. In the same way our prayer is heard, and we have certain forgiveness, not because we have deserved it, but because He has won it all for us and bestowed it upon us. Thus He always remains the only Mediator, through whom we have everything; even that forgiveness which is conditional upon our work of forgiving avails only through Him.
Now you see why Christ attached this addition to the prayer. He did so to establish the closest possible bonds between us and to preserve His Christendom in the unity of the Spirit (Eph. 4:3), both in faith and in love. We must not let any sin or fault divide us or rob us of our faith and of everything else. It is inevitable that there be friction among us every day in all our social and business contacts, where things are said that you do not like to hear and things are done that you cannot stand. This gives rise to anger and discord. We still have our flesh and blood about us, behaving in its own way and easily letting slip an evil word or an angry gesture or action, which is an affront to love. Therefore there must be continual forgiveness among Christians, and we continually need forgiveness from God, always clinging to the prayer: “Forgive us, as we forgive.” That is, unless we are the kind of ungodly people who are always more ready to see a speck in our neighbor’s eye than the log in our own (Matt. 7:3) and throw our own sin behind us. If we were to look at ourselves every day from morning till evening, we would find ourselves so infested that we would forget about other people and be glad that we have a chance to pray.
Luther, M. (1999, c1956). Vol. 21: Luther's works, vol. 21 : The Sermon on the Mount and the Magnificat (J. J. Pelikan, H. C. Oswald & H. T. Lehmann, Ed.). Luther's Works (21:148). Saint Louis: Concordia Publishing House.