Well a big one and not to be taken lightly.
Well for me it's not about 'religion' it really is about 'relationship' and that is the defining difference for me personally.
I have not always been a Christian but now my life in God is the most important thing in the world and is in fact my life.
Therefore as far as I am concerned faith in, and relationship with an all powerful creator God is the most important aspect of my life and everything else is secondary.
That being said I know that God wants me to lead and live a healthy and successful life. This for many people includes a happy, healthy and siccessful marriage.
To answer the question fully; my relationship with God is borne not out of strict and regimented rules and regulations but through grace, this means that I lead my life out of devotion to God through the freedom this grace gives me. I do things God's way not because I have to but because I get to.
The very same goes for marriage and in that, the bible says that a husband should love his wife like Christ loved the church. This ultimately means putting her first (after God of course) and ultimately laying down your life for her, the best example of this coming from Jesus himself. Plus, if my wife is putting God first like I strive to, we are always both on the same page and have the same goals, aspirations and aims.
That isn;t to say that all Christian marriages are perfect, far from it.
It's a bit like a flat pack self assembly desk. You're not going to put it together without looking at the instructions first and as far as I'm concerned God flat packed marriage for us and he holds the instructions.