But I say unto you, That whosoever shall put away his wife, saving for the cause of fornication, causeth her to commit adultery: and whosoever shall marry her that is divorced committeth adultery.
Note 19 at Mt 5:32: Just as with murder (Mt 5:21-22) and adultery (Mt 5:27-28), Jesus was taking divorce one step further than the Mosaic Law did. Under Moses' Law, the people were allowed to get a divorce for any reason (Mt 19:3 and Mr 10:2-4), much as we see today. Divorce was permitted under the Old Testament (as was polygamy) because of the hardness of people's hearts, but Jesus revealed that this was not God's original plan (Mr 10:5-9). Jesus permitted divorce under the New Testament for the sole reason of fornication simply because the fornicator has already broken the union.