A college roommate of mine married a girl of a different faith (not simply of a different Christian denomination). It didn’t work out. After about a dozen years and two children, their “irreconcilable” differences took a fatal toll. It was and is sad for everyone as my wife Sue and I still try to remain friends with both ex-spouses.

I recall, however, that in a conversation shortly after the divorce, the Christian party in this relationship said to me, “The hardest thing was not having Christmas. I think I had a lot of resentment about that.” I will never forget that statement.

Over the years, as I studied theology more and more, I came to appreciate how incredibly formative religion can be. That is, our deepest values and beliefs shape who we come to be. And many of us get those values and beliefs from religion, or from our parents who teach religious beliefs and values.

To attempt to change those beliefs and values or bury them is an exercise in what psychologists call “cognitive dissonance,” where one’s actions do not reflect one’s deeply held values and beliefs. Cognitive dissonance can only go on so long before something breaks. In the case of a mixed-religion marriage, it is the marriage itself that often pays the ultimate price.

You see, when systems of religious belief – assuming they are deeply held and meaningful to those involved – come in conflict in a relationship, someone must give up something if the relationship is to survive. And often, resentment builds in the party that sacrificed their beliefs..

Hole scripture addresses this in St. Paul’s second letter to the church in Corinth. The King James Version (6:14), reads, “Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?” The New American Standard Version is similar, “Do not be bound together with unbelievers; for what partnership have righteousness and lawlessness, or what fellowship has light with darkness?”

While Sue and I do not have oxen, we do have two draft horses which pull wagons down our road. These massive Percheron horses are tied to each other (“yoked”) when they pull. Now, if I used a pony with a Percheron, or if one of them were stronger/weaker or taller/shorter than the other, they will not be able to pull in unison, causing the wagon to go around in circles. Similarly, when oxen are “unequally yoked”, they cannot perform the task set before them. Instead of working together, they are at odds with one another.

St. Paul discouraged the Corinthians from being in an unequal partnership with unbelievers because believers and unbelievers are opposites, just as light and darkness are opposites.

God’s plan is for a man and a woman to become “one flesh” in marriage, a bonding so intimate that one literally and figuratively becomes part of the other. Uniting a believer with an unbeliever is essentially uniting opposites, which makes for a very difficult marriage relationship.

I admit that I am still learning, and perhaps God has more lessons for me on this. And I am humble enough, I hope, to realize that some couples might be able to make this work. What I am saying here is that such a path is very difficult. For certain, what a newly married couple does not need is yet something else that places stress on their marriage.

A few months ago, I met another couple of two different faiths. They are trying to deal with this early on in their marriage, although both admit neither has religious values that are relatively deeply held and neither attends worship regularly.

Their strategy, which is much different from my former roommate’s, is to bring their children up by celebrating both faiths. That sounds very, well, tolerant and open. But sometimes, children trying to understand something as abstract as a supernatural power that cares for them need more than a bunch of holiday celebrations and symbols. They need an identity as one in relationship with a living God.

When we tell children their faith means they should believe all religions, we are telling them something they will soon see is impossible. And when that happens, what becomes of their faith? In the end, to celebrate everything is to celebrate nothing.

Finding a lifelong spouse is increasingly difficult as the world becomes more and more confusing. So, take age-old advice from St. Paul: Be wary of relationships in which the persons are unequally yoked. For the difference, he says, is as plain as light is to darkness.