I have recently come to the conclusion that the exception clause in Matthew 5:32 and 19:9 is not intended to provide a loophole for divorce and remarriage when one of the partners commits adultery.
My Journey to This Conviction
I began, first of all, by being troubled that the absolute form of Jesus' denunciation of divorce and remarriage in Mark 10:11, 12 ("And he said to them, 'Whoever divorces his wife and marries another, commits adultery against her; and if she divorces her husband and marries another she commits adultery against him'") and Luke 16:18 ("Everyone who divorces his wife and marries another commits adultery, and he who marries a woman divorced from her husband commits adultery.") is not preserved by Matthew, if in fact his exception clause is a loophole for divorce and remarriage. I was bothered by the simple assumption that so many writers make that Matthew is simply making explicit something that would have been implicitly understood by the hearers of Jesus or the readers of Mark 10 and Luke 16. Would they really have assumed that the absolute statements included exceptions? I have very strong doubts, and therefore my inclination is to inquire whether or not in fact Matthew's exception clause conforms to the absoluteness of Mark and Luke.
The second thing that began to disturb me was the question, Why does Matthew use the word porneia instead of the word moicheia which means adultery? Almost all commentators seem to make the simple assumption again that porneia means adultery in this context. Even though I am ready to admit that now and then porneia is used in a sense which can include adultery, the question nags at me why Matthew should not use the word for adultery, if that is in fact what he meant. Then I noticed something very interesting. The only other place besides Matthew 5:32 and 19:9 where Matthew uses the word porneia is in 15:19 where it is used alongside of moicheia. Therefore, the primary contextual evidence for Matthew's usage is that he conceives of porneia as something different than adultery. Could this mean, then, that Matthew conceives of porneia in its normal sense of fornication rather than adultery?
The next clue in my search for an explanation came when I stumbled upon the use of porneia in John 8:41 where the Jewish leaders indirectly accuse Jesus of being born of porneia. In other words, since they don't accept the virgin birth, they assume that Mary had committed fornication and Jesus was the result of this act. On the basis of that clue I went back to study Matthew's record of Jesus' birth in Matthew 1:18-20. This was extremely enlightening.
Unlocking a Key Text
In these verses Joseph and Mary are referred to each other as husband (aner) and wife (gunaika). Yet they are described as only being betrothed to each other. This is probably owing to the fact that the words for husband and wife are simply man and woman and to the fact that betrothal was a much more significant commitment then than engagement is today. In verse 19 Joseph resolves "to divorce" Mary. The word for divorce is the same as the word in Matthew 5:32 and 19:9. But most important of all, Matthew says that Joseph was "just" in making the decision to divorce Mary, presumably on account of her porneia, fornication. Therefore, as Matthew proceeded to construct the narrative of his gospel, he finds himself in chapter 5 and then later in chapter 19, in a difficult situation. He has before him the absolute sayings of Jesus that if a man divorces his wife and marries another he commits adultery, that is, he commits a grave injustice.
Nevertheless, the one divorce that Matthew has contemplated with his readers in chapter 1 has been described by him as a "just" possibility. Therefore, in order to avoid the jarring inconsistency between what he has said about Joseph and what Jesus says about divorce, Matthew inserts the exception clause in order to exonerate Joseph and show that the kind of divorce that one might pursue during a betrothal on account of fornication, is not included in what Jesus had said. This interpretation of the exception clause has several advantages: 1) it does not force Matthew to contradict the plain, absolute meaning of Mark and Luke; 2) it provides an explanation for why the word porneia is used in Matthew's exception clause instead of moicheia; 3) it squares with Matthew's own use of porneia for fornication in Matthew 15:19; 4) from a redaction-critical standpoint it is very astute edition which promotes the truth of Jesus' own absolute command and the rightness of Joseph's intention in resolving to divorce his betrothed, Mary.
A Final Argument
There is one more piece of evidence. It is usually assumed by evangelicals that when Jesus said the absolute form of his command, in Luke 18 for example, he was assuming that divorce on account of adultery was taken for granted and that a spouse had the right to remarry when divorced in this way. But there is very strong evidence in Luke 16:18 that Jesus did not assume this but in fact contemplated the possibility of an exception clause and rejected it. Luke 16:18 says, "Everyone who divorces his wife and marries another commits adultery, and he who marries a woman divorced from her husband commits adultery." What is the situation of the woman in the second half of this verse? It seems to me that if we take the verse as a unity (and I can see no reason not to) the situation is that a man has divorced his wife and married another. That is, he has deserted his wife and illegitimately gone off with another and formed a new marital relationship. He has committed adultery against his first wife and left her "divorced." If the traditional view of Matthew's exception clause is correct, then this woman is free to remarry.
But Jesus says just the opposite in the last half of Luke 16:18. He says that the woman who was divorced is not a candidate for remarriage, because if a man marries her, he commits adultery. The only way to escape from this implication is to say that the two halves of the verse don't have anything to do with each other. But against that assumption is the active voice of the word "divorce" in 18a and the passive voice of the word "divorce" in 18b. In other words, the verse pictures a man divorcing in 18a and a woman divorced in 18b and it seems to me completely unnatural to think of this woman divorced in 18a and in 18b as two different women.
The force of this argument has been felt by the translators of the NIV in Matthew 5:32. They translate "anyone who divorces his wife, except for marital unfaithfulness (sic!), causes her to commit adultery, and anyone who marries a woman so divorced commits adultery." The fact that they insert the word "so" shows that they think of the woman in the second half of the verse as the same woman in the first half of the verse. But when they get to Luke 16:18, they simply translate, "Anyone who divorces his wife and marries another woman commits adultery, and the man who marries a divorced woman commits adultery." Why don't they use the word "so" in Luke 16:18? I think the reason is that as soon as they do, it will show that Jesus did consider the situation of an exception clause on the ground of adultery and rejected it. This is in fact the case.
This is what I have taught to my church and I see no warrant for anything different in I Corinthians 7.