Relationships of any nature rise and fall on the ability of the people
in the relationship to
live (deal) with the differences. Younger people tend to worry about
what they have in common with their partners but it is the handling of
differences that makes or breaks relationships.
I have heard it said that One never looks for a partner one can live
with but one looks for a partner they can't life without. The best
test of any relationship is one of adversity. So camping in the rain
and mud is a good one. If people can wake up wet, cold, hungry, not
looking their best from a bad night's sleep and still be an awesome
person, the moment says it all.
Religion doesn't necessarily play a role here because lots of people
marry people who are more or less religious than they are.