WHAT IS MARITAL UNFAITHFULNESS?
Jesus said that the only valid cause for divorce is marital unfaithfulness (Matthew 19:8-9; Mark 10:2-12). Biblical scholars disagree as to whether marital unfaithfulness refers only to physical adultery, or whether it includes other types of unfaithfulness in marriage. This has been the subject of much debate within the church.
Porneia, the word used for marital unfaithfulness in Matthew 19:9, can be used not only of sexual sin in the Bible, but is also used metaphorically for spiritual unfaithfulness (Strong’s Concordance). In the same way, the spiritual unfaithfulness of Israel is described by the Hebrew word, zanah, meaning adultery, or figuratively, idolatry, in numerous instances in the Old Testament (Exodus 34:16; 2 Chronicles 21:11,13; Isaiah 1:21; Jeremiah. 3:8; and Ezekiel 16 and 23).
The following verses also argue against a strictly physical interpretation of marital unfaithfulness:
In Jeremiah 3:8 we see that when the northern tribes of Israel refused to turn from their sin, God divorced them and proclaimed them to be adulterous (using the same word as for "marital unfaithfulness"). Domestic violence is sin; could it also be a type of marital unfaithfulness? Certainly it indicates an unfaithfulness to the basic marital vows to love, honor, and protect.
Why doesn’t the exception for marital unfaithfulness appear in Jesus’ teachings in Mark 10:11-12 or Luke16:18? Here are explanations offered by Guy Duty, a respected biblical scholar, and Herb Vander Lugt, researcher with Radio Bible Class: