“Let marriage be held in honor among all, and let the marriage bed be undefiled; for God will judge the immoral and adulterous” (Heb. 13:4).
This is a sermon concerning the holy estate of matrimony which is highly necessary, especially among Christians, that all men may know what the holy estate of matrimony really is and where it comes from, so that we shall not go on living so casually from day to day, like the heathen and dumb brutes who neither ask nor think about these things, but simply go on interbreeding and cohabiting promiscuously. No, among Christians, it must not be so; but rather as St. Paul says in I Thess. 4 [:3–5], “This is the will of God, your sanctification: that you abstain from immorality; that each one of you know how to take a wife for himself in holiness and honor, not in the passion of lust like heathen who do not know God.”
Therefore Christians should live in sanctification, not like swine and animals, nor like the heathen, who neither regard nor honor this estate. There is much to preach concerning this holy estate and divine ordinance of marriage, for it is the oldest of all estates in the whole world; indeed, all others are derived from that estate in which Adam and Eve, our first parents, were created and ordained and in which they and all their God-fearing children and descendants lived. (“Sermon at Marriage of Sigismund von Luindenau, 1545” (Luther’s Works, v. 51, p.357-358)