This is a huge topic, worthy of a book. I cannot do it justice in this small space. I have tried to touch on the essentials. So while I have tried to present some basic truths I make no pretension of giving the issues involved an exhaustive treatment.
Cooking is what made us human, according to primatologist Richard Wrangham. Cooking food makes it easier to chew and digest. That explains our shorter digestive tract, smaller teeth and jaws, the last two of which made room for our larger brain. The trade-off, however, is that cooking takes longer than just wolfing food down. Who will protect an individual's food from being stolen during this longer process? A strong male. A woman offers her cooking ability and fertility to a strong male who will not only hunt down food but protect their food stores from those who would make off with it. And thus cooking is responsible for marriage! At least according to Wrangham.
It all sounds logical, as do other so-called scientific theories for why other bits of human culture originated. But barring having a time machine to go back and actually ask one of our prehistoric ancestors what their thinking was when they created something, all such modern mind reading must be deemed speculation. Remember that when you hear theories bandied about claiming that belief in the gods goes back to the utility of imagining a movement in the grass was the work of a predator, or that religion was invented by telling gullible people that an invisible entity was watching them to see if they broke the rules when no other human being could see what they were doing.
What we do know is that marriage predates recorded history. In Biblical times, marriage took the form of a covenant, a contract between 2 parties, laying out what each would contribute to the relationship and what each could expect from the other. It was an exchange of promises, the basis of any society. The Ten Commandments are actually stipulations in the covenant between God and the people of Israel. The other laws we see laid down in the books of Exodus through Deuteronomy are specific to the tribes of Israel, which means we must be careful when trying to apply them to modern life in a pluralistic democracy. If a skeptic asks why as a believer you don't stone gays or beat disobedient children with a rod or own slaves, tell him it's because you don't live in the theocratic kingdom of ancient Israel.
Nevertheless, just because a Biblical law addresses a specific situation relevant chiefly to that time and culture doesn't mean that it is totally useless today. There is a principle behind the law and we do well to see how that principle applies to our lives. This is a bit risky, too, because it is an invitation for people to read into the Bible what they want.
With that caveat, let us look at what Jesus says about divorce and remarriage in the Gospels, specifically in Matthew 19:3-9. The Pharisees approach Jesus over an issue that was, even then, a matter of controversy. In Deuteronomy 24, it says that once a man marries a woman "if she finds no favor in his eyes, because he has found some indecency in her," he may divorce her. The problem is what constitutes indecency.
Some rabbis felt that indecency in this context meant fornication, period. More liberal rabbis interpreted it as broadly as possible, so that a man might divorce his wife if she went around with her hair unbound, or spoke with men in the street, both of which were scandalous, or spoke disrespectfully of his parents in his presence or even if she burnt his dinner. Still other rabbis said a man could divorce if he found a woman he liked better and thought to be more beautiful. Considering that a woman had few rights in that culture, this made her position precarious. The only thing that stopped some men was the legal requirement that they must return the dowry, making divorce expensive. Unless the wife was found guilty of adultery, in which case the husband kept it. (Which makes one wonder if the woman taken in adultery and presented to Christ was set up. Where was the man with which she was caught in the act?) So the loose definition of indecency was of more than academic interest.
At first glance, Jesus would seem to agree with the stricter rabbis. Only sexual unfaithfulness excused divorce. But he goes on to say subsequent remarriage on the part of either person was adultery. This eliminates a man's motive to look for an excuse to divorce one wife so he can marry another. And only a man could initiate divorce. But it also put the divorced woman in a worse situation. A woman without a husband had few rights and little power. Though it was uncommon for a man to marry a divorced woman, it did happen.
In going so far, Jesus doesn't actually agree with any of the schools of rabbis. In fact, he goes back to the beginning, to the ideal of marriage as expressed in Genesis 2, where it says that the man and wife become one flesh, or, as C. S. Lewis put it, one organism. They are to regard one another has their other half. That is the underlying principle. But because they are not literally one body, what binds them is marriage as a covenant, an exchange of promises, with responsibilities and expectations on both sides. That made it a powerful metaphor for our relationship with God, one that should not be abandoned, and especially not for reasons less serious than betrayal and unfaithfulness.
Furthermore, Jesus says the exception granted by Moses was a concession, not a commandment. Our focus should be on preserving the principle, not
looking for loopholes.
That said, there is one other reason permitted for divorce in the New Testament. In 1st Corinthians chapter 7, Paul quotes Jesus on the matter of divorce but adds a practical consideration. If an unbeliever leaves his or her Christian spouse, then the believer is no longer bound to the person who left. But aside from adultery or desertion, we have no other grounds for divorce in the New Testament.
What about today? Our state of Florida grants no-fault divorces. Otherwise, the grounds for divorce here are either that the marriage is irretrievably broken or mental incapacity of one of the parties. My wife, for many years a paralegal, doesn't remember ever filling out divorce papers that didn't say that the marriage is irretrievably broken. It's a legal catch-all. It can include everything from no longer being in love to physical abuse.
However, this does point to an important principle. What does one do if a marriage is so broken that it does not function as one anymore? If the promises exchanged are going unfulfilled, the responsibilities and expectations agreed to are unmet, if it is no longer mirroring the love of God, can it still be called a marriage? If you car was so completely broken down that it will never move again on its own power, it can hardly be called a vehicle. Paul points out if one person simply isn't going to stay in the marriage, it is functionally over and the other person can hardly be bound to him or her. Again, this could be seen as a concession to hardness of heart, not a commandment. It could also be considered a mercy.
Let's switch the metaphor. If the two are to become one organism, what does one do if one part of the organism isn't doing its part to protect and nourish and support the growth of the whole, such as in kidney failure? What if, as in abuse, one part of the organism is actively attacking or destroying the other, like a cancer? As C. S. Lewis points out, some churches say that in such circumstances surgery is permitted to separate the two parts of the organism while other churches say that the operation is too dangerous to allow. But all churches see divorce as akin to an amputation, a necessary evil at times, but never simply a neutral option.
As a child of divorce, I can identify with those who say that there is a need for divorce as a desperate measure for desperate situations, rather like a fire axe behind glass, to be used only in a real emergency. But we should never enter into marriage as if there was an free introductory period or a no-obligation "unsubscribe" option. The way to reduce divorces is not to make them harder but to raise, in the eyes of the world, the standards for getting and living married. And it will have to be done by Christians. The secular world only values families in so far as they offer tangible benefits, as a target group for unique consumer goods, as a stabilizing influence on society, as socializing influence on children, as an engine of wealth. So the break up of a family is no more a tragedy than the breakup of a company. After all, many segments of society benefit from divorce. It produces more work for lawyers, more individuals seeking to rent or buy housing, more goods bought to replace those the other partner keeps, more trips to the grocery store, more gifts spent to win the children to your side, more money spent at bars, restaurants and movies seeking new mates, etc.
Only those who understand the spiritual significance of marriage can show that it is more than a cultural custom built up around pair bonding and child rearing. Only we can demonstrate the deeper meaning, the sacramental way in which image of the God who is love is found in human beings coming together, uniting body, mind and spirit in love. We can't do it by focusing on the faulty marriages of others, by pointing out the splinter in the eyes of others while walking around with a log in our own. We can only do this by choosing partners wisely and by loving them faithfully and sacrificially, not selfishly. Jesus said that the world will know we are Christians by our love. It's starts at home, with the person whose bad jokes and bad habits and bad odors you know only too well. When you can see and serve Christ in that person, the world will take notice and desire what you have and another seed of the Gospel will be planted.