This assurance and boast is given us by this text: “Let the marriage bed be undefiled among all.” But this is followed by these words: “God will judge the immoral and adulterous.”

Here is pronounced the judgment that no whoremonger or adulterer will escape God’s judgment. Here our adversaries, the enemies of marriage, must stop, and it will be no help for them to boast and appeal to their vows; for they are the real, true adulterers, who prevent marriage and forbid people to be married. But when our Lord Jesus Christ comes on the last day to judge the living and the dead, God will not judge the married, for they are in his ordinance. Oh, what an unspeakable comfort that is for all married people in their estate! How confidently they can await the glorious coming of our Lord Jesus Christ.  For an apple tree or some other tree which bears its kinds of fruit will not be judged on the last day because it bears apples or is defiled by caterpillars and worms. No, for it was created by God for the purpose of bearing apples and fruit. So married people, who are wedded and bear children and live pure wedded lives, will not be judged because of this.

But the immoral and adulterous, who live outside of this state {of marriage} in defilement and impurity, such as the pope and cardinals, bishops, canons, monks, nuns, etc., who forbid marriage and themselves engage in all kinds of abominable lust and vileness and so woefully befoul the holy estate of matrimony, God will judge on that day. Then the true judgment will be made….(“Sermon at Marriage of Sigismund von Luindenau, 1545” Luther’s Works, v. 51, p.365-366)

Those who bring forth children outside of marriage are parents too, it is true; but there is no honor in it. Therefore it is said, “Let the marriage bed be undefiled.” In other words, let it not be a whore’s bed or an adulterous bed….  St. Paul is … speaking of the purity which should obtain in the marriage estate, that married people should not be fornicators or adulterers and adulteresses. Whatever else occurs in the married state God covers up, for, after all, it is done in order to bring forth children and God approves of this, for it is his ordinance.

This kind of impurity {of fornication}, says God, I do not see {in marriage}. Here parents, fathers and mothers, or married people, are excused; God will not consider it impurity on account of inherited sin, nor will he consider it to be a sin. God will rather build his kingdom of heaven over this work and cover up everything that is unclean in it for the sake of his ordinance and creation.  This is the kind of purity St. Paul means when he says: “Let the marriage bed be undefiled.” He is not talking about cleanness in eating and drinking, but rather about marital faithfulness and duty, in which one trusts the other, keeps away from all other persons, and is content with his own spouse; this is what he calls purity. (“Sermon at Marriage of Sigismund von Luindenau, 1545” Luther’s Works, v. 51, p.364-365)

Here we have a sure and strong word of comfort: “Let marriage be held in honor among all, and let the marriage bed be undefiled.”  Hold fast to that, those of you who are married.

St. Augustine writes in one place concerning married people, that even if one of them is somewhat weak, etc., he should not be afraid of the sudden and infallible Day of the Lord; even if the Day of the Lord were to come in the hour when man and wife were having marital intercourse, they should not be afraid of it. Why is this so? Because even if the Lord comes in that hour he will find them in the ordinance and station in which they have been placed and installed by God.

Now, since this is so, nobody, no mandate of emperor, pope, or bishop, shall stand in my way and prevent me. I am content that I have a gracious God, who is pleased with this ordinance, and who also regards me and blesses and protects me. Who made them so bold and who commanded them to tear down this glorious ordinance of God?… (“Sermon at Marriage of Sigismund von Luindenau, 1545” Luther’s Works, v. 51, p.362-363)

Now we know what the marriage estate is, namely, the creation and ordinance of God, and what is essential to it, namely, a man and a wife. Therefore it should also be considered pure by all men. And if the pope were a Christian, he, too, would hold the marriage estate to be holy and pure. But since he is not a Christian, but the Antichrist and the devil himself, he despises holy matrimony and considers it unclean. But God, who ordained and appointed and blessed the marriage estate, honors marriage. Therefore, we, who are Christians and children of God through faith in Christ, should also honor, uphold, cherish, and esteem the marriage estate. And it should also be kept pure by all; which means that no whore nor adulterer should be found among you, but rather each of you should have his own wife. Moreover, it was for the sake of the marriage estate that God gave us the fourth commandment and made it the first commandment following the first table, thereby declaring that he wants marriage to be upheld and honored, for he says, “Honor your father and your mother, etc.” [Exod. 20:12]. Why should I honor father and mother; after all they lead a carnal life? No, the life father and mother lead is an honorable and godly life. Just as it would be a dishonor for you, if you were born of a whore out of wedlock, so it would be a dishonor if parents lived together unmarried. Therefore to be married is honorable and pleasing to God. But if for a time you have lived outside of this state in concubinage and led a life of fornication, ah, then stop it and repent, enter into marriage and henceforth live a married and godly life. Then you will be doing the right and Christian thing. (“Sermon at Marriage of Sigismund von Luindenau, 1545” Luther’s Works, v. 51, p.364)