Matthew 19 does not permit Divorce in the case of Adultery.

As someone who’s politically a Leftist while being Theologically Conservative I want to clarify this discussion of what The Bible says about Divorce should have no impact on Civil Laws, Civil Marriage as a Legal Contract should have no restriction on how to enter it or leave it (besides Consent and being old enough obviously), forcing people to stay in unhappy marriages is not the way to inspire Christian Morality.

Matthew 19 is the core of why Christian Morality is traditionally Anti-Divorce and yet even the most Conservative commentators are forced to concede Adultery as a valid excuse for Divorce here because of their other Conservative agendas in how to treat a certain word.

Matthew 19:9 in the King James Version uses the word “fornication” for what the only allowable reason for Divorce is.  I’ve proven before on this Blog how that word and the Greek word Pornea are words for specifically Prostitution.  But because casual usage watered down that word to mean any perceived Sexual sin or any sex “outside of marriage” that part of the verse is often quoted as if it used the word Adultery even by people saying they are going off the KJV. 

The problem with thinking that reading is valid is the way even Jesus’s own Disciples reacts to it in verse 10.  Their reaction only makes sense if this is some utterly unprecedented restriction even though Adultery as a good enough reason for divorce is about the most precedented allowance imaginable.

According to the Talmud the Pharisees had an internal disagreement about Divorce at this time, Hillel’s school was more permissive while Shammai allowed it only for Adultery. Jesus seeming more like Shammai here is the exception to the general trend, on everything else Jesus sounds a lot more like Hillel.  But His break from Hillel here is based on very Hillelian principals, Mercy and Forgiveness.

Yes words for Prostitution are often used euphemistically to call someone a whore for being sexually active at all.  But that doesn't change what the word means, the word should be translated as what it means and let the reader interpret how literally it’s being used. And Euphemistic references to Prostitution sometimes go the other way, they are sometimes about the concept of “selling out” and not actually sexual at all.  The core Greek Root behind Pornea means “to sell off” the sex part is not in the actual Etymology.

Adultery is explicitly mentioned in this passage but not as a reason for Divorce, rather as a consequence of it.  This is the only passage in all of Scripture that defines Adultery as a Crime a Husband can commit against his Wife, in The Torah Adultery is always defined only as a Wife sleeping with someone other than her Husband.  Why is explained earlier in Matthew 5:32 where it’s clarified that a Husband causes his Wife to Commit Adultery when he divorces her, because women in that society usually needed a husband to survive.

What does Fornication actually mean?

The word "fornication" was first recorded in Middle English around 1303. It comes from the Latin word "fornix," which literally means "a vault" or "an arch." So what does a vault or an arch have to do with committing fornication? At that particular time in Rome, prostitutes solicited customers in archways. It was like a red light district is today.

Of course, The Bible was not originally written in Latin; it was originally written in Greek, Hebrew, and Aramaic. The first hand-written English language Bible was produced in the 1380's by John Wycliffe. Then came the Gutenberg Bible, the Oxford Bible, Luther's German Bible, the Tyndale New Testament, the Coverdale Bible, the Matthew-Tyndale Bible, the Geneva Bible, and the King James Bible, which was originally published in 1611. Since the word fornication was first used in the early 1300's and continued to be used in the King James Version of the Bible, which is still being used today, it seems logical that these translators spanning over 200 years must have believed that the word fornication had something to do with prostitution; otherwise, they surely would have used a different word.

The Strongs concordance has some problems from being influenced by modern assumptions and indeed what the Strongs Concordance says about "Porneia" Strong# 4202 (the word translated Fornication in the New Testament) is completely wrong and not based on any study of Greek etymology at all.

In Matthew 19:9 The sin of Porneia is the only valid excuse he allows for Divorce, it can't possibly mean simply extramarital sex here. He was asked to intervene in an internal debate between the Pharisees about divorce, but he shocked them all by being more strict then any sect of the Pharisees expected.  All the Pharisees agreed that Adultery was a valid reason for divorce. The Shammai camp believed that adultery was the only valid reason, while Hillel allowed many others. Jesus was usually inline with Hillel's way of thinking but here he made an exception, he was shockingly to the right of even Shammai.

Some people think it means here Pre-Martial sex, or finding out the bride wasn't a virgin. But Jesus was all about forgiveness and not holding things against people, he would never condemn a bride for a pre-existing condition, that'd be even worse then allowing it for adultery.

Prostitution is the sin Gomer the wife of Hosea was guilty of and for which he divorced her.  The only time in The Bible a divorce happens because God instructs it.  But in the long run God prefers forgiveness even for this offense.  The story is ultimately an analogy to Israel's spiritual Adultery and Prostiution with other gods.

People often tie this into Deuteronomy 24:1, especially if they want to say Jesus wasn't really doing away with The Law but clarifying it.   But it was in chapter 22 that Deuteronomy dealt with if a husband accuses his bride of not being a virgin.

Defilement in Deuteronomy could refer to anything in Leviticus 18, as well a prostitution.  Jesus made it clear his teaching on divorce was about how it was only to appease man it was allowed under The Law of Moses at all.

That Gomer's sin is what Jesus meant is the most Biblically sound and logical conclusion from using Scripture to interpret Scripture.

Porneia derives from pernaō, which means "to sell off". Putting that meaning in a sexual context clearly means Prostitution. Another related word used in The Bible is

Pornos (por'-nos); Word Origin: Greek,  Noun Masculine, Strong #: 4205 a man who prostitutes his body to another's lust for hire a male prostitute

Which is 5 times translated "Fornicator" but 5 other times "Whoremonger" which typically means one who visits prostitutes. King James English simply didn't know how to communicate the idea of a male Prostitute, Gigolo wasn't coined yet.

Also

Porne (por'-nay); Word Origin: Greek,  Noun Feminine, Strong #: 4204 a woman who sells her body for sexual uses a prostitute, a harlot, one who yields herself to defilement for the sake of gain an idolatress of "Babylon", the chief seat of idolatry

8 times translated Harlot and 4 times Whore in the KJV.

So as you can see, it's about Prostitution, not simply any and all sexual activity one doesn't like.

1 Corinthians 6:13 and up when talking about Fortification explicitly defines it "shall I then take the members of Christ, and make them the members of an harlot? God forbid. What? know ye not that he which is joined to an harlot is one body? for two, saith he, shall be one flesh."

Revelation 17 also used Fornication to describe the allegorical Prostitution of the Whore of Babylon.

Now sometimes words affiliated with prostitution are casually used more loosely to express disapproved of sexual behavior. A Biblical passage where that might be how it's being used is in Jude when discussing Sodom and the Pre-Flood world. But again premarital sex isn't the issue there. And it certainly is possible prostitution was going on too.  Actually Ezekiel 16 when talking about Sodom clearly mentions prostitution.

John 8:41 is one of the few verses where they're obviously using it loosely, but it's the villains of the narrative using it there, believers are supposed to understand everything they say to be wrong on every level.

But sexual acts with not actual financial translation isn't the only way we use words for prostitution euphemistically.   We also say things like "whoring myself out" to refer to the idea of "selling out".

Now I've seen some argue that New Testament usage of certain Greek words should be understood by how the Septuagint (The Hellenistic era Greek translation of the Old Testament) used them. Well to begin with the Septuagint is very flawed, and I feel the assumption that early Christian, and specifically NT authors where always following it is also flawed. Our main existing Septuagint manuscripts come from Christian copyists, so we should be careful what we assume about places where the LXX and the New Testament seem to match.

Now, I can't easily check how the Septuagint used Pornea. But I do know that all 5 occasions where the KJV of the OT used "Fornication", it's one of 2 Hebrew Words. Zanah (Strong# 2181) or Taznuwth (Strong# 8457). Both words that the majority of the times the KJV translated something like Whoredom, "go a whoring", Whore, Harlot, Whorish, and so on.

So again, there is no Biblical basis for the word meaning anything more then Prostitution.

1 Corinthians 5 verse 1 is a passage that one might consider the Achilles heel of arguing the word only means prostitution. "It is reported commonly that there is fornication among you, and such fornication as is not so much as named among the Gentiles, that one should have his father's wife." Paul uses the word, but then specifies he's talking about a type of Incest.

First of all this is still a specific Sin specifically addressed in Leviticus 18. So it is still hardly enough to argue that the word means "everything" the way "Fornication" has come to mean to modern pharsiees.

Even if it did mean "sexual immorality" (as many modern Bibles translate it) we'd still have to use the greater testimony of Scripture to determine what is sexually immoral. I have a separate study on that, and with the help of the Song of Solomon I refute the notion that all none reproductive sex is a sin. And argue that it's mostly reproductive sex God wanted to restrict, though Prostitution and Pagan sex acts have other reasons for being deemed a sin.

Secondly, we don't know the full details of this situation.

 Since we're still in the first generation of Christianity, all Paul's readers were likely not born into the faith, so this individual's father's wife, may likely have been an unbeliever. Which leads back to the fact that Prostitution in the Bible is often used symbolically of Idolatry. That's what the "Strange Woman" discussed repeatedly in Proverbs is really, about, all the words translated "Strange" there mean Pagan or Heathen (foreign in a spiritual sense).

So I'd argue the only way in which The Bible would approve of loosening the definition of Prostitution is in the context of Believers getting involved with Unbelievers.

And at any-rate, as I discus elsewhere, ritual Prostitution was known to be going on in Corinth. Some scholars have seen an allusion to that here, but that's speculative.

Those verses where it might seem to casually be used more loosely are not passages that define sexual sin, they're  simply stating that "Porneia" is/was going on somewhere. So just because you can cite a verse as seeming to mean more then just "Paying money for sex" doesn't mean you can then just jump to saying it means "Everything but sex between a husband and wife". Even today our using words like "whore" loosely does not change that when someone specifically says they disapprove of prostitution they clearly mean paying money for sex.

Originally Fornication was a perfectly accurate translation of the meaning of this word. Man has simply abused it since 1611.