The question often comes up when discussing the "remarriage exception" in Matthew 19. What exactly is sexual immorality/fornication? The original word is "inappropriate contenteia" where we get our word inappropriate contentography.
I wrote this up in regards to views on the remarriage text, but it may give some insights here too.
Here is the text in question:
Mat 19:8 He said to them, "Because of your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so.
Mat 19:9 And I say to you: whoever divorces his wife, except for sexual immorality, and marries another, commits adultery."
Jesus statement suggests he was clarifying the law found in Deut. 24 in which they were permitted to divorce if indecency (uncleanness in KJV) was found in her.
Deu 24:1 "When a man takes a wife and marries her, if then she finds no favor in his eyes because he has found some indecency in her, and he writes her a certificate of divorce and puts it in her hand and sends her out of his house, and she departs out of his house
(Strong's)
ערוה
‛ervâh
er-vaw'
From H6168; nudity, literally (especially the pudenda) or figuratively (disgrace, blemish): - nakedness, shame, unclean (-ness).
Now the question is, what was entailed by this indecency (Deut) or sexual immorality/adultery/fornication (Matthew).
The term used in the exception clause is the oft-debated term inappropriate contenteia. You can look up all of its uses using Strongs etc. Here are some of the more interesting ones:
Mat 15:19 For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false witness, slander.
Gal 5:19 Now the works of the flesh are evident: sexual immorality, impurity, sensuality
These texts use both inappropriate contenteia and the more specific word, Moixeia which always means adultery. In fact, in Jesus statement in Matthew 19 He uses both as well. The grounds for divorce and remarriage were inappropriate contenteia and the resulting sin if this was not present was causing them to commit adultery, moichatai.
This indicates that either inappropriate contenteia was distinct from adultery or was a broader word that also included adultery.
(Strong's)
inappropriate contenteia
por-ni'-ah
from G4203; harlotry (including adultery and incest); figuratively idolatry: - fornication.
μοιχεία
moicheia
moy-khi'-ah
From G3431; adultery: - adultery.
The next text of interest is I Corinthians 7.
1Co 7:1 Now concerning the matters about which you wrote: "It is good for a man not to have sexual relations with a woman."
1Co 7:2 But because of the temptation to sexual immorality, each man should have his own wife and each woman her own husband.
Here is it is clear that marriage was intended partly as a means to help resist sexual immorality (inappropriate contenteia) by unmarried people. In other words, if you are lusting, get married. Here fornication is used of the unmarried probably in the sense of sex outside of marriage.
Act 15:20 but should write to them to abstain from the things polluted by idols, and from sexual immorality, and from what has been strangled, and from blood.
In the Acts council they enforced upon the gentiles the same requirements already made of strangers (ie. Gentiles) living among the Israelites in the law. The sexual immorality mentioned in Acts is spelled out in its various forms in Leviticus. The list includes acts done while married (wifes sister) which would be problematic both as adultery and as having sex with close relations. It does seem that Leviticus 18 clarifies the term sexual immorality. I am not sure it is strictly limited to just the things mentioned, but a lot are mentioned that qualify.
Requirements of strangers
Eating blood:
LEV 17:10 " `Any Israelite or any alien living among them who eats any blood--I will set my face against that person who eats blood and will cut him off from his people. 11 For the life of a creature is in the blood, and I have given it to you to make atonement for yourselves on the altar; it is the blood that makes atonement for one's life. 12 Therefore I say to the Israelites, "None of you may eat blood, nor may an alien living among you eat blood."
Sexual immorality:
LEV 18:6 " `No one is to approach any close relative to have sexual relations. I am the LORD.
LEV 18:7 " `Do not dishonor your father by having sexual relations with your mother. She is your mother; do not have relations with her.
LEV 18:8 " `Do not have sexual relations with your father's wife; that would dishonor your father.
LEV 18:9 " `Do not have sexual relations with your sister, either your father's daughter or your mother's daughter, whether she was born in the same home or elsewhere.
LEV 18:10 " `Do not have sexual relations with your son's daughter or your daughter's daughter; that would dishonor you.
LEV 18:11 " `Do not have sexual relations with the daughter of your father's wife, born to your father; she is your sister.
LEV 18:12 " `Do not have sexual relations with your father's sister; she is your father's close relative.
LEV 18:13 " `Do not have sexual relations with your mother's sister, because she is your mother's close relative.
LEV 18:14 " `Do not dishonor your father's brother by approaching his wife to have sexual relations; she is your aunt.
LEV 18:15 " `Do not have sexual relations with your daughter-in-law. She is your son's wife; do not have relations with her.
LEV 18:16 " `Do not have sexual relations with your brother's wife; that would dishonor your brother.
LEV 18:17 " `Do not have sexual relations with both a woman and her daughter. Do not have sexual relations with either her son's daughter or her daughter's daughter; they are her close relatives. That is wickedness.
LEV 18:18 " `Do not take your wife's sister as a rival wife and have sexual relations with her while your wife is living.
LEV 18:19 " `Do not approach a woman to have sexual relations during the uncleanness of her monthly period.
LEV 18:20 " `Do not have sexual relations with your neighbor's wife and defile yourself with her.
LEV 18:21 " `Do not give any of your children to be sacrificed to Molech, for you must not profane the name of your God. I am the LORD.
LEV 18:22 " `Do not lie with a man as one lies with a woman; that is detestable.
LEV 18:23 " `Do not have sexual relations with an animal and defile yourself with it. A woman must not present herself to an animal to have sexual relations with it; that is a perversion.
LEV 18:24 " `Do not defile yourselves in any of these ways, because this is how the nations that I am going to drive out before you became defiled. 25 Even the land was defiled; so I punished it for its sin, and the land vomited out its inhabitants. 26 But you must keep my decrees and my laws. The native-born and the aliens living among you must not do any of these detestable things, 27 for all these things were done by the people who lived in the land before you, and the land became defiled. 28 And if you defile the land, it will vomit you out as it vomited out the nations that were before you.
Idols
Lev 17:3 If any one of the house of Israel kills an ox or a lamb or a goat in the camp, or kills it outside the camp,
Lev 17:4 and does not bring it to the entrance of the tent of meeting to offer it as a gift to the LORD in front of the tabernacle of the LORD, bloodguilt shall be imputed to that man. He has shed blood, and that man shall be cut off from among his people.
Lev 17:5 This is to the end that the people of Israel may bring their sacrifices that they sacrifice in the open field, that they may bring them to the LORD, to the priest at the entrance of the tent of meeting, and sacrifice them as sacrifices of peace offerings to the LORD.
Lev 17:6 And the priest shall throw the blood on the altar of the LORD at the entrance of the tent of meeting and burn the fat for a pleasing aroma to the LORD.
Lev 17:7 So they shall no more sacrifice their sacrifices to goat demons, after whom they harlot. This shall be a statute forever for them throughout their generations.
Lev 17:8 "And you shall say to them, Any one of the house of Israel, or of the strangers who sojourn among them, who offers a burnt offering or sacrifice
Lev 17:9 and does not bring it to the entrance of the tent of meeting to offer it to the LORD, that man shall be cut off from his people.
It appears that inappropriate contenteia could carry a number of connotations. Adultery, incest, pre-marital sex, etc.
So with this information in mind the question comes up, what did Jesus mean by his exception clause? There are a couple of main views:
a. Main protestant view: Only literal, physical adultery would release someone from the marriage and allow for remarriage.
b. Catholic View: There are no grounds for divorce except for an non-sacramental marriage in the first place, which would indicate pre-marital fornication, or a marriage based on incest, etc. Here is one exposition of it. You can see how it matches with your understanding.
http://members.aol.com/johnprh/marriage.html ).
Here is a protestant from my own denomination with a view very similar to the Catholic one. Fornication previous to the marriage that was later discovered would allow for divorce and subsequent remarriage. However, adultery after the start of the marriage would not be grounds for divorce.
http://www.lifeheritage.org/Divorce%20and%20Remarriage.pdf
This view has some advantages.
a. It upholds Jesus admonition that the one flesh should not be put apart.
b. It explains better what was meant by the divorce allowance in Deut. There had to be an uncleanness found afterward (but presumable starting before). Some of the pharisees aparently interpreted uncleanness very broadly.
Depending on how you handle inappropriate contenteia it could be referring to a non-lawful marriage, but the word itself is not related to "lawful" as such.
