In verse 3, it says: 

"Some Pharisees came to him to test him. They asked, 'Is it lawful for a man to divorce his wife for any and every reason?'"

I think one of the most important parts of this passage is the description of the Pharisees motive in inquiring about divorce. Like in many other places, their objective was to test Christ. 

Content of the Law? Or Reason for the Law?

In light of seeing their motive, Christ's first response doesn't actually answer the question (which he knew was a trap), but rather takes aim at the fundamental concern behind the question. The Pharisees were primarily concerned with what the *rules* were ("Is it lawful?"). 

No doubt, in Christ's day, all the different sects of Judaism must have been arguing about how to interpret the Torah (the Law of Moses). 

But as is clear to me now, Christ was interested in a far more interesting question. 

And so he responded: 

"Haven’t you read," he replied, "that at the beginning the Creator ‘made them male and female,’ and said, ‘For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh’? So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate." (verses 4-6)

So what is Jesus doing here with this answer? 

He's taking the listener back in time and forcing them to consider a more fundamental question than the one they were asking, which is:

Why is there a marriage custom/law to begin with?

And his answer to his own question, is essentially that the union between a man and a woman is a very mysterious one where two individual humans become "one flesh", or in a sense, one person. In other words, they become "intertwined" and connected, on a very deep level. 

And this "union" is how the human race was "designed"/made to be, and is the nexus from which children ought to be born. In more modern/scientific terms, we would call this "pair-bonding". And this "bond" is a deeply psychological/spiritual/ chemical etc bond that can't be easily broken, that is, without causing extreme distress. 

No doubt among other psychological factors, modern science has recognized a peptide hormone called "oxytocin" that plays a role in "bonding" a man and a woman together.

So instead of answering their question about the law, or the "rule", Jesus pointed them back in time, and pointed out that: "Hey! Maybe there is a really good reason for the rule to begin with! 

If Two People Become "One Flesh", What Then of Divorce?

In light of this original ideal, and the nature of the union of marriage, the Pharisees then asked what to them would have been a pretty obvious next question:

"Why then,” they asked, “did Moses command that a man give his wife a certificate of divorce and send her away?” (verse 7)

They're essentially saying "If marriage is such a strong union and connection, why allow divorce at all then?" Jesus then, with his authority and insight, responded: 

“Moses permitted you to divorce your wives because your hearts were hard. But it was not this way from the beginning. I tell you that anyone who divorces his wife, except for sexual immorality, and marries another woman, commits adultery.” (verses 8-9)

This answer of course is very important, and it is where many people (including myself) have misunderstood Christ, and taken him far too literally, with not enough nuance (and suffered the consequences of unjustified guilt and shame). So let's try and illuminate what Christ is really getting at here. 

A New Rule about Marriage and Divorce?

I used to read this verse fairly straight-forwardly (like reading a newspaper), without considering the context, and why Jesus said what he did. In essence, I took Jesus as saying this: 

"Here's the old rule you guys have been following. But I have come to give you a NEW RULE!"

I see now that this interpretation couldn't have been further from the truth. The one thing that Jesus was not doing in this verse, was laying down a new "rule" for people to follow, at least not at the fundamental/essential level.

He's essentially tempting the listener to a question: 

"If pair-bonding/marriage is such a strong and binding thing, what does that imply about the nature of divorce?"

And the answer to that question should then become pretty apparent to us: Ripping apart that union has tremendously difficult immediate and long-term practical consequences, of which we should all be wary. 

"Because Your Hearts Were Hard"?

And now we can get to Jesus' direct answer of "Moses permitted you to divorce your wife because your hearts were hard". 

Let's first explain what this does not mean. He was not saying that if anyone ever initiates a divorce, that it implies that the initiator necessarily has a "hard heart". He is not saying that you should never get a divorce, lest it be found out about you that you have a hard heart and are a bad person. In fact, this has very little to do with the initiator of the divorce (who could be doing so for a whole myriad of reasons, good or bad).

Jesus is essentially saying this (paraphrased):

"Moses permitted you to divorce your wives because of the hardness of people's hearts, which tragically, sometimes, made divorce necessary."

Yes, Jesus is basically admitting here that, tragically, because your "hearts were hard", divorce, with all it's heartache and misery and displacement, was sometimes necessary. 

The "hardness of hearts" Christ referred to, was the state of mind people get into, where they are so stubbornly committed to all manner of destructive attitudes and behaviours, where it makes it impossible for their partners to continue on in a union with them. And so then they are stuck in a situation where they have to choose between two "evils"; to continue in the destruction/abuse/adultery of their partner, or leave, and suffer the heartache of that separation. Both options are horrific, but tragically, divorce/separation is sometimes better, or a "lesser of evils".

And that's why Christ then immediately followed it up with 

"but it was not this way from the beginning."

He's essentially juxtaposing our fallen world, where divorce is sometimes tragically necessary, with the original ideal of how, in light of what the marriage union was/is, since the beginning. And how, in light of this, being concerned about what "the law" says, is just really short-sighted. 

"Causes Her to Commit Adultery", or "Commits adultery"?

It's the next sentence of Jesus that really confused me though for quite sometime. 

It was as if Jesus is being unequivocal about interpreting the "rules" laid out in the law of Moses:

In Matthew 19:9, he says: "I tell you that anyone who divorces his wife, except for sexual immorality, and marries another woman, commits adultery."

But we need to compare this with another passage in Matthew where Christ addresses the same issue, but with a slightly different answer. In Matthew 5:31, Jesus says "whoever divorces his wife...causes her to commit adultery". 

In order to understand this, we need to keep in mind the immediate textual context described above, and the way that Jesus uses the word "adultery". It should be more apparent now from the context that he doesn't mean it in the same way as the Pharisees were caught up with; which was a moralizing-based rule. But we can see in the original greek (from greek scholars), that Jesus was using the passive version of the word "adultery", and that passive sense implies a lot!

And this passive sense is also illuminated by the cultural context. It's important to understand the state of affairs that women lived under in Greco-Roman times. Unlike the modern west, there was no help for women from the State. There were no welfare programs, women's programs, child benefits, etc. And to make matters worse, a woman's word in the law system was worth much less than a man's. For women, a divorce could imply the destruction of her way of life, and even possibly death!

A woman in this situation would feel immediate pressure to marry another man almost right away, because for her, that meant security and safety from poverty/death.

So we can see then that Christ is taking issue with the Pharisees' preoccupation with the "rules", and how they are not even apparently considering the welfare of the divorced woman, who would be subject to immense difficulty immediately after receiving a "certificate of divorce". It's the coldness of the Pharisees that is the real concern to Christ here. 

And so to summarize, there are two things which illuminate the meaning here: 

• The word "adultery", in the greek, is in the passive sense.
  
• The cultural context tells us that a newly divorced woman would often be in extreme danger, and would be pressured to immediately marry someone else for her own safety (would be forced into "adultery"). 
  

"Adultery" in a Non-Moralizing Sense?

And this brings us to the conclusion. In light of Christ's emphasis on the nature of the "one flesh"/pair-bonding nature of the union between a man and a woman, and in light of the practical danger that he was highlighting of the woman being pushed into a dangerous situation where she would basically often be forced into being with someone who she was not "bonded" with (and all it's subsequent destruction/danger), it becomes clear that Christ's use of the word "adultery", is not the same as how the Pharisees were using it. 

He was not laying down a new rule. He was challenging the listener to think more deeply about what exactly the union between a man and a woman is, on a practical level. 

What is pair-bonding? What is the spiritual/psychological/biological nature of a man and a woman becoming "one flesh"? 

Once one considers these deeper questions, the silliness of the original question (pressing about the "rule") becomes a little more plain. And the danger of taking the marriage/sexual union lightly, also becomes plain. 

Christ's use of the word "adultery", obviously now, is referring to the consequences (physical, spiritual, psychological, etc) of the breaking of a deep union. It has very little to do with "moral rules", or "obeying God".

Christ is warning us that, once you've "pair-bonded" with someone else, that union cannot be broken without causing damage. It doesn't matter how much you don't like the person, or even if they are causing you great pain. Breaking a union has severe consequences, which we should all try avoid as much as possible.

Now that Christ has pointed us back to the more original questions, we may then find ourselves saying along with the Pharisees: 

"If this is the case, it is better not to marry!"

And Christ would no doubt also say to us in return: 

"Let him who can accept this, accept it."