Matthew 19:9

Perhaps some one will say, that Jesus in thus speaking, suffered wives to be put away for the same cause that Moses suffered them, which He says was for the hardness of the hearts of the Jews. But to this it is to be answered, that if by the Law an adulteress is stoned, that sin is not to be understood as the shameful thing for which Moses suffers a writing of divorcement; (Deut. 24:1.) for in a cause of adultery it was not lawful to give a writing of divorcement. But Moses perhaps calls every sin in a woman a shameful thing, which if it be found in her, a bill of divorcement is written against her. But we should enquire, If it is lawful to put away a wife for the cause of fornication only, what is it if a woman be not an adulteress, but have done any other heinous crime; have been found a poisoner, or to have murdered her children? The Lord has explained this matter in another place, saying, Whoso putteth her away, except for the cause of fornication, maketh her to commit adultery, (Mat. 5:32.) giving her an opportunity of a second marriage.

"But I say unto you, Whosoever shall put away his wife except it be for fornication, and marry another, committeth adultery." For since he had stopped their mouths, He then gives the law with His own authority, like as touching the meats, like as touching the Sabbath. For with regard to the meats likewise, when He had overcome them, then, and not till then, He declared unto the multitude, that, "Not that which goeth in defileth the man;" and with regard to the Sabbath, when He had stopped their mouths, He saith, "Wherefore it is lawful to do well on the Sabbath day;" and here this self-same thing.

It is fornication alone which destroys the relationship of the wife; for when she has divided one flesh into two, and has separated herself by fornication from her husband, she is not to be retained, lest she should bring her husband also under the curse, which Scripture has spoken, He that keepeth an adulteress is a fool and wicked. (Prov. 18:23.) For it might be that a man might falsely charge an innocent wife, and for the sake of another woman might fasten an accusation upon her. Therefore it is commanded so to put away the first, that a second be not married while the first is yet alive. Also because it might happen that by the same law a wife would divorce her husband, it is also provided that she take not another husband; and because one who had become an adulteress would have no further fear of disgrace, it is commanded that she many not another husband. But if she do marry another, she is in the guilt of adultery; wherefore it follows, And whoso marrieth her that is put away, committeth adultery.

(De Conjug. Adult. ii. 9.) For a reunion of the wedlock, even after actual commission of adultery, is neither shameful nor difficult, where there is an undoubted remission of sin through the keys of the kingdom of heaven; not that after being divorced from her husband an adulteress should be called back again, but that after her union with Christ she should no longer be called an adulteress.

Therefore said He well, Moses suffered, not commanded. For what we command, that we ever wish; but when we suffer, we yield against our will, because we have not the power to put full restraint upon the evil wills of men. He therefore suffered you to do evil that you might not do worse; thus in suffering this he was not enforcing the righteousness of God, but taking away its sinfulness from a sin; that while you did it according to His law, your sin should not appear sin. For as he is cruel and unjust that puts away a chaste wife, so is he a fool and unjust that retains an unchaste; for in that he hides the guilt of his wife, he is an encourager of foulness. For every thing by whatsoever causes it is created, by the same is it destroyed. It is not matrimony but the will that makes the union; and therefore it is not a separation of bodies but a separation of wills that dissolves it. He then who puts away his wife and does not take another is still her husband; for though their bodies be not united, their wills are united. But when he takes another, then he manifestly puts his wife away; wherefore the Lord says not, Whoso putteth away his wife, but, Whoso marrieth another, committeth adultery.