Matthew 19:9

‘And I say to you, Whoever shall put away his wife, except for fornication, and shall marry another, commits adultery, and he who marries her when she is put away commits adultery.” '

Thus in God's eyes if a man puts away his wife and marries another he commits adultery. And anyone who marries the wife who is divorced also commits adultery. Both are sinning grievously against God. Note the, ‘I say to you' (compare its repetition in chapter 5). This dictum has the authority of Jesus behind it.

There is, however, one exception to the rule, and that is where porneia has been committed. This word is wider than just fornication and adultery and is used to cover different kinds of sexual misbehaviour (see 1 Corinthians 5:1; 1 Corinthians 5:13; Ephesians 5:3; Colossians 3:5). Thus if there has been fornication of one of the parties to a marriage with an outside party before the marriage was finalised that would justify divorce, for strictly from God's viewpoint that person would be seen as married to that other. It would include adultery, for such adultery would break the marriage bond, thus releasing from it the ‘innocent' party in the same way as the death of the guilty party would (which was strictly required according to the Law). It could include bestiality (lying with an animal) for that too would break the marriage bond. It would probably include acts of lesbianism or homosexuality.

We should note that this ‘exception' actually strengthens the significance of marriage. The exception arises because one of the parties has sinfully broken the marriage by an act which has made them in God's eyes liable to die. Thus the idea is that the ‘innocent' party can treat them as being ‘dead' in God's eyes. They are ‘cut off'. They are no longer within God's covenant. Divorce from them therefore maintains the sanctity of marriage.

This exception was especially important for Matthew because a Jew (and therefore often a Christian Jew) saw adultery not only as a grounds for divorce but as actually requiring divorce. Adultery was seen as an unredeemable blot on the marriage. For Mark and Luke in writing to Gentiles it did not have quite the same importance and they therefore do not refer to it. They wanted rather to stress the permanence of marriage. But all would have agreed that adultery destroys a marriage for it is the equivalent of an act of remarriage (1 Corinthians 6:16).

But in all our discussion about divorce we must not here lose sight of the fact that Jesus is laying down a new ‘interpretation of the Law' under the Kingly Rule of Heaven (compare on Matthew 5:27). He is beginning to introduce His new world. And this radical change with regard to marriage is a first step in the process.