Matthew 5:31,32 (Luther)

Matthew 5:31. It was also said, “Whoever divorces his wife, let him give her a certificate of divorce.”
32. But I say to you that everyone who divorces his wife, except on the ground of unchastity, makes her an adulteress; and whoever marries a divorced woman commits adultery.

Here you get a good picture of the violence they did to the commandment in order to provide themselves with enough room and freedom to transgress it and yet to avoid the charge of sin. All that really mattered was that a person was not too flagrant in committing overt acts of adultery. If he had developed an aversion to his wife and wanted to get rid of her and if he had acquired a desire for another woman, he was permitted to desert his wife and to have an affair with another woman whom he liked better. If this woman already had a husband, it was a simple matter to make him give her up and put her away without it being said that he had been forced to do so. Among them it was also a minor matter if a man took another woman to bed with him and thus made her his wife, for they would have liked to have more than one wife anyway. So far, in fact, had the situation progressed that in matters of marriage and divorce everyone acted pretty much as he pleased, without being ashamed or having a bad conscience about it. For this reason Christ also takes up this matter of divorce. He salts and rebukes the scandalous way they abuse the permission of divorce, and He instructs their consciences on the kind of procedure in this question which is proper and which does not go beyond or against the commandment. He touches on it only very briefly here; later on (Matt. 19:3–9) He discusses it in greater detail.
What is the proper procedure for us nowadays in matters of marriage and divorce? I have said that this should be left to the lawyers and made subject to the secular government. For marriage is a rather secular and outward thing, having to do with wife and children, house and home, and with other matters that belong to the realm of the government, all of which have been completely subjected to reason (Gen. 1:28). Therefore we should not tamper with what the government and wise men decide and prescribe with regard to these questions on the basis of the laws and of reason. Christ is not functioning here as a lawyer or a governor, to set down or prescribe any regulations for outward conduct; but He is functioning as a preacher, to instruct consciences about using the divorce law properly, rather than wickedly and capriciously, contrary to God’s commandment. Here, therefore, we will not go beyond an examination of their situation and a consideration of the proper behavior of people who lay claim to the name “Christian.” The non-Christians are no concern of ours, since they must be governed, not with the Gospel, but with compulsion and punishment. Thus we shall keep our ministry clear and not claim any more right than we are authorized to have.
In Deuteronomy 24:1 we read: “When a man takes a wife and marries her, if then she finds no favor in his eyes because he has found some indecency in her, he should write her a bill of divorce and send her out.” But immediately (Deut. 24:4) it adds the prohibition that if later on the same man would like to have her back, he “may not take her again to be his wife.” They were quick to learn this law and eager to abuse it. As soon as a man got tired of his wife and developed a desire for another, he immediately discarded and dismissed her, though Moses had permitted this only on the grounds that “he found some indecency in her” which prevented them from staying together. They had taken many liberties on this question, till they themselves saw that what they were doing was no credit to them and that frequently it was quite frivolous. Therefore they asked Christ, Matthew 19: “Is it lawful to divorce one’s wife for any cause?” His answer to them is a severe sermon, the likes of which they had never heard before, coming to the same conclusion as He did here: Except for the cause of fornication, both he who divorces a woman and he who pays court to a divorced woman are guilty of adultery and are making her guilty of adultery, too, if she takes another man; for if she did not have a man again, she could not be guilty of adultery. So He not only rebukes them for their frivolity in the question of divorce, but He teaches them not to get a divorce at all, or if they do get one, to remain unmarried on both sides. And He comes to the conclusion that divorce is always an occasion for adultery.
They asked (Matt. 19:7): “Why, then, did Moses permit such divorces?” He answers (Matt. 19:8): “For your hard hearts Moses allowed you to divorce your wives. It is still not a good thing to do; but since you are such wicked and unmanageable people, it is better to grant you this much than to let you do worse by vexing or murdering each other or by living together in incessant hate, discord, and hostility.” This same thing might even be advisable nowadays, if the secular government prescribed it, that certain queer, stubborn, and obstinate people, who have no capacity for toleration and are not suited for married life at all, should be permitted to get a divorce. Since people are as evil as they are, any other way of governing is impossible. Frequently something must be tolerated even though it is not a good thing to do, to prevent something even worse from happening.
So it is settled now. Those who want to be Christians should not be divorced, but every man should keep his own spouse, sustaining and bearing good and ill with her, even though she may have her oddities, peculiarities, and faults. If he does get a divorce, he should remain unmarried. We have no right to make marriage a free thing, as though it were in our power to do with as we pleased, changing and exchanging. But the rule is the one Christ pronounces (Matt. 19:6): “What God has joined together, let no man put asunder.” The only source of trouble here is the fact that marriage is not thought of on the basis of the Word of God, as His work and ordinance, and that His will is ignored. He has given every man his spouse, to keep her and for His sake to put up with the difficulties involved in married life. To them it seems to be nothing more than a purely human and secular state, with which God has nothing to do. Therefore they tire of it so quickly; and if it does not go the way they would like, they immediately want a divorce and a change. Then God so arranges things that they are no better off as a consequence. A person who wants to change and improve everything and who refuses to put up with any inadequacies, but insists on having everything clean and comfortable, will usually get in exchange something twice as uncomfortable or ten times as uncomfortable. This is a general rule, not only in this matter but in all others as well.
So it must be on earth. Daily there have to be many troubles and trials in every house, city, and country. No station in life is free of suffering and pain, both from your own, like your wife or children or household help or subjects, and from the outside, from your neighbors and all sorts of accidental trouble. When a person sees and feels all this, he quickly becomes dissatisfied, and he tires of his way of life, or it makes him impatient, irritated, and profane. If he cannot avoid this trouble or get rid of it, he wants to change his station in life, supposing that everyone else’s station and condition are better than his own. After changing around for a long time, he discovers that his situation has progressively deteriorated. A change is a fast and easy thing, but an improvement is a rare and doubtful thing. This was what the Jews found out, too, as they divorced and changed their marriage partners.
In this area, therefore, we should do what we have always taught and exhorted: If you want an undertaking of yours to be blessed and successful, even a temporal undertaking like getting married or staying home or accepting a position, lift up your voice to God, and call upon the One who owns it and who has to grant it. It is no small gift from God to find a wife who is pious and easy to get along with. Then why not ask Him to make it a happy marriage? For your initial desire and your curiosity will not give you either happiness or stability, unless He adds His blessing and success and helps you to bear the occasional troubles. Those who do not do this, therefore, who rush into things on their own as though they did not need God’s help, and who do not learn how to make certain allowances—they get exactly what they deserve. They have sheer purgatory and the torments of hell inside them, and that without any help from the devil. They do not bear their trouble patiently. They have selected only what seems to be just right to them, and they have tried to abolish and annul the article called “forgiveness of sin.” Therefore their reward is a restless and impatient heart; thus they have to suffer double trouble and have no thanks for it. But we have said enough about this elsewhere.
But you ask: “Then is there no legitimate cause for the divorce and remarriage of a man and his wife?” Answer: Both here and in Matthew 19:9 Christ sets down only one, called adultery; and He cites it on the basis of the Law of Moses, which punishes adultery with death (Lev. 20:10). Since it is only death that can dissolve a marriage and set you free, an adulterer has already been divorced, not by men but by God Himself, and separated not only from his wife but from this very life. By his adultery he has divorced himself from his wife and has dissolved his marriage. He had no right to do either of these, and so he has brought on his own death, in the sense that before God he is already dead even though the judge may not have him executed. Because it is God that is doing the divorcing here, the other partner is set completely free and is not obliged, unless he chooses to do so, to keep the spouse that has broken the marriage vow.
We neither commend nor forbid such divorces, but leave it to the government to act here; and we submit to whatever the secular law prescribes in this matter. To those who really want to be Christians, we would give this advice. The two partners should be admonished and urged to stay together. If the guilty party is humbled and reformed, the innocent party should let himself be reconciled to him and forgive him in Christian love. Sometimes there is no hope for improvement, or the reconciliation of the guilty one and his restoration to good graces is followed only by his abuse of this kindness. He persists in his flagrant and loose behavior and takes it for granted that he is entitled to be spared and forgiven. I would not advise or prescribe mercy for a person like that; rather I would help to have such a person flogged or jailed. For one oversight is still pardonable, but a sin that takes mercy and forgiveness for granted is intolerable. Anyway, as we have said, we know that no one should be compelled to take back a public prostitute or an adulterer if he does not want to do so or is so disgusted that he cannot do so. We read (Matt. 1:19) that although Joseph was a pious man, he was not willing to take Mary, his betrothed wife, when he saw that she was pregnant; and he is praised for being “resolved to divorce her quietly” instead of registering a complaint against her and having her executed, as he had a right to do.
An additional cause for divorce is this: when one spouse deserts the other, that is, when he runs away out of sheer peevishness. For example, if a pagan woman were married to a Christian man, or as happens sometimes nowadays, if one spouse is an Evangelical and the other is not, is divorce legitimate in such a case? Paul discusses the matter in 1 Corinthians 7:13–15 and comes to this conclusion: if the one partner consents to remain, the other partner should keep him; even though they may not be one in matters of faith, the faith should not dissolve the marriage. If it happens that the other partner simply refuses to remain, then let him go; you have no duty or obligation to go with him. But it sometimes happens now that one of these good-for-nothings deserts his wife without her knowledge or consent, leaving his house and home, wife and children, and staying away two or three years or as long as he feels like staying away. When he has sown his wild oats and squandered his property, he decides he would like to return home and pick up where he had left off. And now the other partner should be obliged to wait for him as long as he feels like staying away and then to take him back?! Such a good-for-nothing should not only be barred from his house and home, but also banished from the country. If he refuses to come after a summons and a decent interval of waiting, the other partner should be set completely free. Such a person is much worse than a heathen and an unbeliever (1 Tim. 5:8); he is less tolerable than a wicked adulterer, who fell once but can still improve and be as faithful to his wife as he had been before. But this person treats marriage just as he pleases. In his wife and children he does not recognize the obligations of domestic life and duty, but takes it for granted that he will be received if the notion takes him to return. This is how it should be: Whoever wants to have a wife and children must stay with them; he must bear the good and the ill with them as long as he lives. If he refuses to do so, he should be told that he must; otherwise he will be separated from wife, house, and home permanently. Where these causes are not present, other faults and foibles should not be a hindrance to marriage, nor a reason for divorce, things like quarrels or other trouble. But if there is a divorce, says St. Paul, both partners should remain unmarried.
This much in brief on what the text says about this business; elsewhere I have written enough about it.40 As I have said, the best way to prevent divorce and other discord is for everyone to learn patience in putting up with the common faults and troubles of his station in life and to put up with them in his wife as well, knowing that we can never have everything just right, the way we would like to have it. Even the condition of your own body can never be any different or better. You have to put up with the many kinds of filth and discomfort that it causes you every day; and if you were to throw away everything about it that is impure, you would have to start with the belly, which you need to nourish you and to keep you alive.
Now, you can stand it when your body emits a stench before you realize it, or when it festers and becomes pussy and completely pollutes your skin. You make allowances for all this. In fact, this only increases your concern and love for your body; you wait on it and wash it, and you endure and help in every way you can. Why not do the same with the spouse whom God has given you, who is an even greater treasure and whom you have even more reason to love? For the love among Christians should be the same kind of love as that of every member of the body for every other one, as St. Paul often says (Rom. 12:4, 5; 1 Cor. 12:12–26), each one accepting the faults of the other, sympathizing with them, bearing and removing them, and doing everything possible to help him. Hence the doctrine of the forgiveness of sins is the most important of all, both for us personally and for our relations with others. As Christ continually bears with us in His kingdom and forgives us all sorts of faults, so we should bear and forgive one another in every situation and in every way. Whoever refuses to do this, may God grant him no rest and make his misfortune or plague ten times as bad.
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 (21:92). Saint Louis: Concordia Publishing House.