You ought to thank the almighty, eternal God, the Father of our Lord Jesus Christ, that you can boast of the ordinance of God and the holy estate of matrimony. Keep it and raise up your children in the name of God. You don’t need to worry about whether you are condemned by God for it, nor will he judge you for the work’s sake; this I know for certain. Indeed, the fact that you are married, as long as you are a Christian, will be a great glory and honor to you on the last day. And now, and as long as you live, be confident in every hour that you are living in an estate which was instituted by God and is pleasing to him. Let pope and bishops who are opposed to it fulminate and growl and the more they boast of their vow and condemn the married state the more let us be proud of the ordinance of God in which we live, for this God and his only Son, our Lord Jesus Christ, and the Holy Spirit, is and will remain an everlasting God, whereas the pope and his rabble will wither like the grass of the field or quickly vanish away like a bubble.

But it is also required that every Christian should remain in the estate and calling in which he has been placed by God and faithfully discharge its duties; then God adds felicity and blessing. May God grant us this and be praised to all eternity. Amen. (“Sermon at Marriage of Sigismund von Luindenau, 1545” Luther’s Works, v. 51, p.366-367)

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)