Thou shalt not commit adultery.
These commandments now [that follow] are easily understood from [the explanation of] the preceding; for they are all to the effect that we [be careful to] avoid doing any kind of injury to our neighbor. But they are arranged in fine [elegant] order. In the first place, they treat of his own person. Then they proceed to the person nearest him, or the closest possession next after his body namely, his wife, who is one flesh and blood with him, so that we cannot inflict a higher injury upon him in any good that is his. Therefore it is explicitly forbidden here to bring any disgrace upon him in respect to his wife. And it really aims at adultery, because among the Jews it was ordained and commanded that every one must be married. Therefore also the young were early provided for [married], so that the virgin state was held in small esteem, neither were public prostitution and lewdness tolerated (as now). Therefore adultery was the most common form of unchastity among them.
But because among us there is such a shameful mess and the very dregs of all vice and lewdness, this commandment is directed also against all manner of unchastity, whatever it may be called; and not only is the external act forbidden, but also every kind of cause, incitement, and means, so that the heart, the lips, and the whole body may be chaste and afford no opportunity, help, or persuasion to unchastity. And not only this, but that we also make resistance, afford protection and rescue wherever there is danger and need; and again, that we give help and counsel, so as to maintain our neighbor's honor. For whenever you omit this when you could make resistance, or connive at it as if it did not concern you, you are as truly guilty as the one perpetrating the deed. Thus, to state it in the briefest manner, there is required this much, that every one both live chastely himself and help his neighbor do the same, so that God by this commandment wishes to hedge round about and protect [as with a rampart] every spouse that no one trespass against them.
But since this commandment is aimed directly at the state of matrimony and gives occasion to speak of the same, you must well understand and mark, first, how gloriously God honors and extols this estate, inasmuch as by His commandment He both sanctions and guards it. He has sanctioned it above in the Fourth Commandment: Honor thy father and thy mother; but here He has (as we said ) hedged it about and protected it. Therefore He also wishes us to honor it, and to maintain and conduct it as a divine and blessed estate; because, in the first place, He has instituted it before all others, and therefore created man and woman separately (as is evident), not for lewdness, but that they should [legitimately] live together, be fruitful, beget children, and nourish and train them to the honor of God.
Therefore God has also most richly blessed this estate above all others, and, in addition, has bestowed on it and wrapped up in it everything in the world, to the end that this estate might be well and richly provided for. Married life is therefore no jest or presumption; but it is an excellent thing and a matter of divine seriousness. For it is of the highest importance to Him that persons be raised who may serve the world and promote the knowledge of God, godly living, and all virtues, to fight against wickedness and the devil.
Therefore I have always taught that this estate should not be despised nor held in disrepute, as is done by the blind world and our false ecclesiastics, but that it be regarded according to God's Word, by which it is adorned and sanctified, so that it is not only placed on an equality with other estates, but that it precedes and surpasses them all, whether they be that of emperor, princes, bishops, or whoever they please. For both ecclesiastical and civil estates must humble themselves and all be found in this estate as we shall hear. Therefore it is not a peculiar estate, but the most common and noblest estate, which pervades all Christendom, yea which extends through all the world.
In the second place, you must know also that it is not only an honorable, but also a necessary state, and it is solemnly commanded by God that, in general, in all conditions, men and women, who were created for it, shall be found in this estate; yet with some exceptions (although few) whom God has especially excepted, so that they are not fit for the married estate, or whom He has released by a high, supernatural gift that they can maintain chastity without this estate. For where nature has its course, as it is implanted by God, it is not possible to remain chaste without marriage. For flesh and blood remain flesh and blood, and the natural inclination and excitement have their course without let or hindrance, as everybody sees and feels. In order, therefore, that it may be the more easy in some degree to avoid unchastity, God has commanded the estate of matrimony, that every one may have his proper portion and be satisfied therewith; although God's grace besides is required in order that the heart also may be pure.
From this you see how this popish rabble, priests, monks, and nuns, resist God's order and commandment, inasmuch as they despise and forbid matrimony, and presume and vow to maintain perpetual chastity, and, besides, deceive the simple-minded with lying words and appearances [impostures]. For no one has so little love and inclination to chastity as just those who because of great sanctity avoid marriage, and either indulge in open and shameless prostitution, or secretly do even worse, so that one dare not speak of it, as has, alas! been learned too fully. And, in short, even though they abstain from the act, their hearts are so full of unchaste thoughts and evil lusts that there is a continual burning and secret suffering, which can be avoided in the married life. Therefore all vows of chastity out of the married state are condemned by this commandment, and free permission is granted, yea, even the command is given, to all poor ensnared consciences which have been deceived by their monastic vows to abandon the unchaste state and enter the married life, considering that even if the monastic life were godly, it would nevertheless not be in their power to maintain chastity, and if they remain in it, they must only sin more and more against this commandment.
Now, I speak of this in order that the young may be so guided that they conceive a liking for the married estate, and know that it is a blessed estate and pleasing to God. For in this way we might in the course of time bring it about that married life be restored to honor, and that there might be less of the filthy, dissolute, disorderly doings which now run riot the world over in open prostitution and other shameful vices arising from disregard of married life. Therefore it is the duty of parents and the government to see to it that our youth be brought up to discipline and respectability, and when they have come to years of maturity, to provide for them [to have them married] in the fear of God and honorably; He would not fail to add His blessing and grace, so that men would have joy and happiness from the same.
Let me now say in conclusion that this commandment demands not only that every one live chastely in thought, word, and deed in his condition, that is, especially in the estate of matrimony, but also that every one love and esteem the spouse given him by God. For where conjugal chastity is to be maintained, man and wife must by all means live together in love and harmony, that one may cherish the other from the heart and with entire fidelity. For that is one of the principal points which enkindle love and desire of chastity, so that, where this is found, chastity will follow as a matter of course without any command. Therefore also St. Paul so diligently exhorts husband and wife to love and honor one another. Here you have again a precious, yea, many and great good works, of which you can joyfully boast, against all ecclesiastical estates, chosen without God's Word and commandment.