I am borrowing this from a post I made on another thread.
The discussion of the text in Matthew 5:32 concerning divorce because of sexual sin needs some additional perspective. Please note that each of the synoptic gospels were written to different audiences. For example Matthew was written primarily to the Jews while Mark was written to gentiles. As a result, they have some differences. It is noteworthy that Mark’s gospel when quoting Jesus on divorce does not include the exception for divorce due to unchastity or sexual sin. There is a reason that this difference exists.
Scripture is a “high context” set of documents. If we take Mark’s gospel we come to the conclusion that there is no exception and divorce is always forbidden. If we read Matthew we know there is an exception. Matthew included the exception because of Jewish understandings at the time of Jesus. If a women was involved in illicit sexual activity during the bethrothal period or returned to such activity after being married the Jews saw this as a reason for divorce. Jesus recognizes this situation for what it is, and some translations of Matthew’s gospel give recognition to it as well. The following translations should make this clear:
– Young’s Bible
Matthew 5:32 but I say to you, that whoever may put away his wife, save for the matter of whoredom, doth make her to commit adultery; and whoever may marry her who hath been put away doth commit adultery.
– New Jerusalem with Apocrypha
Matthew 5:32 But I say this to you, everyone who divorces his wife, except for the case of an illicit marriage, makes her an adulteress; and anyone who marries a divorced woman commits adultery.
The Church recognizes the Jewish context of Matthew’s gospel and also sees the importance of no exceptions from Mark’s gospel. A marriage is either valid or invalid depending on the disposition and intent of the marital partners. The Church has been generous in granting annulments when the data supports them, but the Church cannot undo a valid marriage.
Further discussion might also be given to the Pauline privilege and its relationship to the words of Jesus about divorce.
I hope this helps.