....let us go to part two of his paper "The Estate Of Marriage" circa 1522
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three grounds for divorce. The first, is the situation in which the husband or wife is not equipped for marriage because of bodily or natural deficiencies of any sort.
The second ground is adultery. Here you see that in the case of adultery Christ permits the divorce of husband and wife, so that the innocent person may remarry. For in saying that he commits adultery who marries another after divorcing his wife, "except for unchastity," Christ is making it quite clear that he who divorces his wife on account of unchastity and then marries another does not commit adultery.
Some are spiritual, teaching righteousness in the sight of God, such as love and obedience; people who obeyed these commandments did not thrust away their wives and never made use of certificates of divorce, but tolerated and endured their wives' conduct.
Others are worldly, however, drawn up for the sake of those who do not live up to the spiritual commandments, in order to place a limit upon their misbehaviour and prevent them from doing worse and acting wholly on the basis of their own maliciousness.
Accordingly, he commanded them, if they could not endure their wives, that they should not put them to death or harm them too severely, but rather dismiss them with a certificate of divorce. This law, therefore, does not apply to Christians, who are supposed to live in the spiritual government. In the case of some who live with their wives in an un-Christian fashion, however, it would still be a good thing to permit them to use this law, just so they are no longer regarded as Christians, which after all they really are not.
Thus it is that on the grounds of adultery one person may leave the other, as Solomon also says in Proverbs 18, "He that keepeth an adulteress is a fool". We have an example of this in Joseph too. In Matthew 1 [:19] the gospel writer praises him as just because he did not put his wife to shame when he found that she was with child, but was minded to divorce her quietly. By this we are told plainly enough that it is praiseworthy to divorce an adulterous wife. If the adultery is clandestine, of course, the husband has the right to follow either of two courses. First, he may rebuke his wife privately and in a brotherly fashion, and keep her if she will mend her ways. Second, he may divorce her, as Joseph wished to do. The same principle applies in the case of a wife with an adulterous husband. These two types of discipline are both Christian and laudable.
You may ask: What is to become of the other [the guilty party] if he too is perhaps unable to lead a chaste life? Answer: It was for this reason that God commanded in the law [Deut. 22: 22-24] that adulterers be stoned, that they might not have to face this question. The temporal sword and government should therefore still put adulterers to death, for whoever commits adultery has in fact himself already departed and is considered as one dead.
Therefore, the other [the innocent party] may remarry just as though his spouse had died, if it is his intention to insist on his rights and not show mercy to the guilty party. Where the government is negligent and lax, however, and fails to inflict the death penalty, the adulterer may betake himself to a far country and there remarry if he is unable to remain continent. But it would be better to put him to death, lest a bad example be set.