“In the second place, after God had made man and woman he blessed them and said to them, “Be fruitful and multiply” [Gen. 1:28]. From this passage we may be assured that man and woman should and must come together in order to multiply. Now this [ordinance] is just as inflexible as the first, and no more to be despised and made fun of than the other, since God gives it his blessing and does something over and above the act of creation. Hence, as it is not within my power not to be a man, so it is not my prerogative to be without a woman. Again, as it is not in your power not to be a woman, so it is not your prerogative to be without a man. For it is not a matter of free choice or decision but a natural and necessary thing, that whatever is a man must have a woman and whatever is a woman must have a man.
For this word which God speaks, “Be fruitful and multiply,” is not a command. It is more than a command, namely, a divine ordinance [werck] which it is not our prerogative to hinder or ignore. Rather, it is just as necessary as the fact that I am a man, and more necessary than sleeping and waking, eating and drinking, and emptying the bowels and bladder. It is a nature and disposition just as innate as the organs involved in it. Therefore, just as God does not command anyone to be a man or a woman but creates them the way they have to be, so he does not command them to multiply but creates them so that they have to multiply. And wherever men try to resist this, it remains irresistible nonetheless and goes its way through fornication, adultery, and secret sins, for this is a matter of nature and not of choice” (Luther’s Works, vol. 45, p.18).