My sister asked the above profound question. She doesn't know the Lord Jesus. It was referenced toward a family we know where the couple seems miserable.
Apologetics aren't my strong suit. I think I answered her incompletely. I figured I'd give it a second try and with more time for the thoughts to brew.
Sweet sister of mine, marriage is hard. When two selfish people move into the same space with all their expectations of what married life is going to be like... it's a recipe for disaster.
In a way, it's like siblings who share a room. At some point when nothing is going your way and you're angry at your sister for talking on the phone for hours when you have a major test the next day and are so tired: you're going to walk over and beat your sister on the head with the blasted telephone. (not that I would know anything about something like that...)
The difference with siblings is that we already sort of know each others personality and know how their going to react because we've lived with them since the younger one's birth. That gives us the advantage at intentionally pushing each others buttons... but it also gives us the advantage of knowing how to avoid accidentally pushing those buttons.
In marriage, we don't know those expectations. Some of them are silly. Derek expected me to rinse my toothpaste spit out of the sink with water when we got married. That was something that wasn't expected of us when we were growing up, so I didn't know to do it. We actually fought about toothpaste spit! I learned to clean up my mess because it bothered him; he learned that it was silly to expect me to clean up without telling me about that expectation.
So therein lies the problem: two selfish people who don't know every expectation that their spouse has move under the same roof and sin in anger. That is what creates misery in marriage: selfish expectations. I think that's probably the issue with the couple we talked about.
Miserable Christians like our example family are probably staying married because of expectations. Expectations from family and friends to stay married. Expectations and rules from the Bible to stay married. Expectations and fear of failure.
But that is not how Christian marriage should be.
You see, if we're truly walking with the Spirit, then we should be dying to ourselves. Dying to our selfish expectations and learning to serve our spouses.
Remember when you were here, sweet sister, and I got so angry at Bronwyn while I was making dinner. I can't even remember what she was doing. But I do remember that I was hungry and that I expected her to stay out of my way so I could satisfy my hunger. You know what happened after I yelled at her and you removed her from the room? The Spirit convicted me of my selfish sin. He pointed out that I had mistreated her and that I was failing to love and serve her because I wanted what I wanted now (food). I still remember apologizing to Bronwyn for my sin in your presence.
That above process is what makes Christians who love Jesus and are dying to ourselves daily, stay married. It's called Sanctification: the process of being made to be more like Jesus. It's hard. It's humbling. It's not commonly felt, seen, or practiced. And it's especially hard to see since so many 'Christians' are simply following a set of rules/expectations rather than pursuing loving Jesus and others in every possible way.
Does that help you understand? I'm not trying to judge our question provoking couple, but I would say that they haven't reached this place of humbling themselves to love their spouse on a daily basis despite their own selfish expectations. And I think that's sad, because there's a sweet joy found in humbling yourself within marriage that isn't found anywhere else in life.