“Thus the doctors {of theology} have found three good and useful things about the married estate, by means of which the sin of lust, which flows beneath the surface, is counteracted and ceases to be a cause of damnation.
First, …. It is an outward and spiritual sign of the greatest, holiest, worthiest, and noblest thing that has ever existed or ever will exist: the union of the divine and human natures in Christ….
Second, [the doctors say] that marriage is a covenant of fidelity. The whole basis and essence of marriage is that each gives himself or herself to the other, and they promise to remain faithful to each other and not give themselves to any other. By binding themselves to each other, and surrendering themselves to each other, the way is barred to the body of anyone else, and they content themselves in the marriage bed with their one companion. In this way God sees to it that the flesh is subdued so as not to rage wherever and however it pleases, and, within this plighted troth, permits even more occasion than is necessary for the begetting of children. But, of course, a man has to control himself and not make a filthy sow’s sty of his marriage.…” (Luther’s Works, vol. 44, p.9-12).