One thing that keeps me in a consistent state of awe regarding the Bible is how clearly God's standards and ways are expressed in Scripture. This happens partly because I think there is an entire industry that exists to find ways to make the clear less-than-clear while also using the less-than-clear to build personal kingdoms. Some of that, though, is another sermon for another day.
Rather, let's dig back into Mark and take a look at Mark 10 (link). Here are few of the stories in this chapter:
First, you have a few of the Pharisees trying to get Jesus to settle one of their disputes. The Pharisees, to their credit, wanted to get the Law of God exactly perfect so they could obey it. The Pharisees, to their discredit, seemed to believe that they were better than anyone else for this effort and that God liked them better, too. One of the Pharisaic debates at the time was over divorce.
Back in the Old Testament, when Moses gathered from God the laws to govern Israel, divorce had been permitted. The law, though, was vague and only stated that a man was to write a certificate of divorce for his wife and send her away. It did not address the idea of causes or reasons for divorce. So, two basic views arose: one was that the law was permissive, that as long as you wrote the certificate, you could have a divorce. The other was restrictive: there had to be a reason, something based in the portions of the law that related to finding your newly-married bride was not what she should have been, to get a divorce. These two groups were the main lines of thought about divorce at the time.
Since this was a big deal, much like divorce and marriage are now, the Pharisees were assured that if Jesus sided with one side or the other, He would be angering a large contingent of the people. Should He side with the "wide-open" group, those who had struggled to make their marriage work or who thought this was a wicked, loose moral position would pounce on Him. So, too, would the groups of women who were disadvantaged in that society because of capricious divorce. Yet if He takes the stronger position, many would find Him being excessively legalistic and attack Him for that. After all, is this man not speaking much of grace? Plus, that puts Him adding to the words of Moses, which would have been more fuel for their fire.
Except Jesus does not truly side with either side. Instead, His response is this: the reason you guys want the divorce answer? It's because your hearts are hard and sinful. My Creation was this: a man and a woman marry, starting a new relationship of unity, and it lasts for their entire life.
He turns the whole problem on its head and points out that the Pharisees were, really, looking at the wrong issue. They wanted to know how to get out of a marriage. The real question, the real problem, was this: they were not paying attention to how to get into a marriage in the first place.
They were not supposed to go in while looking for the exit doors, but rather go in looking to glorify and honor God by holding true to their commitments. Instead, they were looking in marriage only for what would benefit them—whether they wanted to bail out for any cause or only if they found something "inappropriate" about their wives.
Marriage in the Scriptural ideal is one man, one woman, married to each other for life. This is what we should be striving toward in Christian community, teaching the next generation to seek this. To make this their commitment when they come down the aisle.
Does that make anything else unforgivable? Heavens no. Yet one area that we have got to mature in the American Church is this: we have to learn to acknowledge sin as being sin while knowing that grace abounds. We have to be mature enough to admit when even our own lives have gone down a sinful path without trying to excuse it or make it "off-limits" and something that cannot be spoken of.
One certain way to keep a cycle of failing marriages is this: never speak of the importance of marrying to honor God in the first place, and never speak of divorce as bad. That way, no one feels guilty for what has happened, but no one grows up enough to make sure it does not happen again.
Today's Nerd Note: More of an EMPHASIS point: Marriage is intended as a lifetime commitment between two people with a sinful nature. It may be a redeemed sinful nature, and ought to be. Christians ought only marry those who share their faith.
There are things that happen, though, that wreck this covenantal relationship, and man does render asunder what God has joined together. Further, there are people who seem one way and turn out differently, and that difference is violent and dangerous. The totality of the ethics of the situation are more than I will address here: you should seek spiritual counsel from those whom you trust. I will say this: life is too precious. Each human on this earth is made in the image of God, and no portion of obeying God regarding marriage should put your life at risk against your will. (I know some missionary couples who jointly risk their lives, and this is obedience.)
However, if one spouse is threatening bodily harm against the other, the right course of action is to find a safe place and remain, as best you can, in a place of safety. I believe that God can change the vilest offender, but God can do so through your prayers from another state. No amount of my belief that the marriage covenant is intended for a lifetime should be taken to mean that one spouse has the right to threaten (or take) the life of their spouse to get out. Nor that it is the responsibility of a spouse to "take it" for the sake of the marriage. Get safe. Get God-honoring counsel and pray for healing and restoration, but do it from a place of safety.