You must know also that marriage is not only an honorable but also a necessary state. In general and in all conditions it is solemnly commanded by God that men and women, who were created for marriage, shall be found in this estate. Yet there are some exceptions (although few) whom God has especially set apart. They are not fit for the married estate. Or there are individuals whom He has released by a high, supernatural gift so that they can maintain chastity without this estate [Matthew 19:11–12]. 212 For where nature has its course—since it is given by God—it is not possible to remain chaste without marriage [1 Corinthians 7]. For flesh and blood remain flesh and blood. The natural desire and excitement have their course without delay or hindrance, as everybody sees and feels. In order, therefore, that it may be easier in some degree to avoid inchastity, God has commanded the estate of marriage. In this way everyone may have his proper portion and be satisfied with it. Yet God’s grace is also required in order that the heart may be pure.
In short, even though they abstain from the act, their hearts are so full of unchaste thoughts and evil lusts that there is a continual burning and secret suffering, which can be avoided in the married life [1 Corinthians 7:9]. 216 Therefore, all vows of chastity outside of the married state are condemned by this commandment. Free permission to marry is granted.
Now, I speak of this in order that the young may be guided so that they desire the married estate and know that it is a blessed estate and pleases God. For in this way, over time we might cause married life to be restored to honor. There might be less of the filthy, loose, disorderly behavior that runs riot the world over in open prostitution and other shameful vices arising from disregard for married life. 218 Therefore, it is the duty of parents and the government to see to it that our youth are brought up with discipline and respectability. When they have become mature, parents and government should provide for them to marry in the fear of God and honorably. God would not fail to add His blessing and grace, so that people would have joy and happiness from marriage.
——Martin Luther (Book of Concord, Large Catechism, Sixth Commandment)