For me, the question of whether or not living a religious lifestyle benefits marriage can only be answered in the affirmative. I have seen many people I love struggle through and end their marriages when their previously-strong commitment to God waned; it seems that losing faith in Him starts people on the path of losing faith in many things.
I believe that has a lot to do with just how deeply-rooted religion and spirituality can become in one who practices them. In most religions, there are commandments believers are meant to follow, one or more divine beings they’re supposed to worship, and other believers they’re likely to pattern their own lifestyle after. For many religious people, myself included, our faith is our way of life, and necessarily affects all our behaviors to some degree.
For those who fall out of love with their religion, then, it is unsurprising when their marriages are in jeopardy. Their entire way of life is upset, and it’s likely that they begin to question everything. That sort of damage can be (and often is) catastrophic.
Regarding couples I have met in which one or both members were not particularly religious, my experience is admittedly limited. But in cases where only one spouse was religious, I have seen that it’s often a point of contention or, at the very least, an issue over which the religious spouse worries and even weeps. Where both members of the couple are non-religious, I have yet to find a pair that didn’t seem wishy-washy or selfishly-motivated.
In conclusion, I feel that religion fosters an abiding and resounding level of commitment in its subscribers. And, in a world where so much of life is driven by “I” and “me”, it is comforting to see how much power comes from couples who have already lived much of their lives believing they were part of something much greater than their individual selves.