“You are not to commit adultery.”
 The following commandments are easily understood from the preceding one, for they all teach us to guard against harming our neighbor in any way. They are admirably arranged. First they deal with the person of our neighbors. Then they go on to speak of the person nearest to them, the most important thing to them after their own life, namely, their spouse, who is one flesh and blood with them. With respect to no other blessing can one do them greater harm than here. Therefore, it is explicitly forbidden here to dishonor another’s marriage partner.  Adultery is particularly mentioned because among the Jewish people it was ordered and commanded that one marry. Young people were married at the earliest age possible, and the state of virginity was not commended, nor were public prostitution and lewdness tolerated as they are now. Accordingly, adultery was the most widespread form of unchastity among them.
 But inasmuch as there is such a shameless mess and cesspool of all sorts of immorality and indecency among us, this commandment is also directed against every form of unchastity, no matter what it is called. Not only is the outward act forbidden, but also every kind of cause, provocation, and means, so that your heart, your lips, and your entire body may be chaste and afford no occasion, aid, or encouragement to unchastity.  Not only that, but you are to defend, protect, and rescue your neighbors whenever they are in danger or need, and, moreover, even aid and assist them so that they may retain their honor.  Whenever you fail to do this (although you could prevent a wrong) or do not even lift a finger (as if it were none of your business), you are just as guilty as the culprit who commits the act.  In short, all are required both to live chastely themselves and also to help their neighbors to do the same. Thus God wants to guard and protect every husband or wife through this commandment against anyone who would violate them.
 However, because this commandment is directed specifically toward marriage as a walk of life and gives occasion to speak of it, you should carefully note, first, how highly God honors and praises this walk of life, endorsing and protecting it by his commandment. He endorsed it above in the Fourth Commandment, “You shall honor father and mother.” But here, as I said, he has secured and protected it.  For the following reasons he also wishes us to honor, maintain, and cherish it as a divine and blessed walk of life. He has established it before all others as the first of all institutions, and he created man and woman differently (as is evident) not for indecency but to be true to each other, to be fruitful, to beget children, and to nurture and bring them up to the glory of God.  God has therefore blessed this walk of life most richly, above all others, and, in addition, has supplied and endowed it with everything in the world in order that this walk of life might be richly provided for. Married life is no matter for jest or idle curiosity, but it is a glorious institution and an object of God’s serious concern. For it is of utmost importance to him that persons be brought up to serve the world, to promote knowledge of God, godly living, and all virtues, and to fight against wickedness and the devil.
 Therefore I have always taught that we should not despise or disdain this walk of life, as the blind world and our false clergy do, but view it in the light of God’s Word, by which it is adorned and sanctified. Because of this Word it is not a walk of life to be placed on the same level with all the others, but it is before and above them all, whether those of emperor, princes, bishops, or any other. Important as the spiritual and civil walks of life are, these must humble themselves and allow all people to enter marriage as a walk of life, as we shall hear.  It is not a restricted walk of life, but the most universal and noblest, pervading all Christendom and even extending throughout all the world.
 In the second place, you should also remember that it is not just an honorable walk of life but also a necessary one; it is solemnly commanded by God that in general both men and women of all walks of life, who have been created for it, shall be found in this walk of life. To be sure, there are some (albeit rare) exceptions whom God has especially exempted, in that some are unsuited for married life, or others God has released by a high, supernatural gift so that they can maintain chastity outside of marriage.  Where nature functions as God implanted it, however, it is not possible to remain chaste outside of marriage; for flesh and blood remain flesh and blood, and natural inclinations and stimulations proceed unrestrained and unimpeded, as everyone observes and experiences. Therefore, to make it easier for people to avoid unchastity in some measure, God has established marriage, so that all may have their allotted portion and be satisfied with it—although here, too, God’s grace is still required to keep the heart pure.
 From this you see that our papal crowd—priests, monks, and nuns—resist God’s ordinance and commandment when they despise and forbid marriage and boast and vow that they will maintain perpetual chastity while they deceive the common people with lying words and false impressions.  For no one has so little love and inclination for chastity as those who under the guise of great sanctity avoid marriage and either indulge in open and shameless fornication or secretly do even worse—things too evil to mention, as unfortunately has been experienced all too often.  In short, even though they abstain from the act, yet their hearts remain so full of unchaste thoughts and evil desires that they suffer incessant ragings of secret passion, which can be avoided in married life.  Therefore, all vows of chastity outside marriage are condemned and annulled by this commandment; indeed, all poor, captive consciences deceived by their monastic vows are even commanded to forsake their unchaste existence and enter the married life. In this regard, even if the monastic life were godly, still it is not in their power to maintain chastity. If they remain in it, they will inevitably sin more and more against this commandment.
 I say these things in order that our young people may be led to acquire a desire for married life and know that it is a blessed and God-pleasing walk of life. Thus it may in due time regain its proper honor, and there may be less of the filthy, dissolute, disorderly conduct that is now so rampant everywhere in public prostitution and other shameful vices resulting from contempt of married life.  Therefore parents and governmental authorities have the duty of so supervising the youth that they will be brought up with decency and respectability and, when they are grown, will be married honorably in the fear of God. Then God would add his blessing and grace so that they might have joy and happiness in their married life.
 Let it be said in conclusion that this commandment requires all people not only to live chastely in deed, word, and thought in their particular situation (that is, especially in marriage as a walk of life), but also to love and cherish the spouse whom God has given them. Wherever marital chastity is to be maintained, above all it is essential that husband and wife live together in love and harmony, cherishing each other wholeheartedly and with perfect fidelity. This is one of the chief ways to make chastity attractive and desirable. Under such conditions chastity always follows spontaneously without any command. This is why St. Paul so urgently admonishes married couples to love and honor each other.  Here again you have a precious good work—indeed, many great works—in which you can happily boast over against all “spiritual walks of life” that are chosen without God’s Word and commandment.