One major compatibility aspect of marriage is religion. This mostly deals with the dating period versus marriage. It is very important to be of the same or similar religion. When all the butterflies are flying it's easy to smooth over differences of faith and think rose colored glasses will be enough. Not quite so.
Religion is a very personal root that often guides our perspective and actions in life. It helps govern our priories. When there are people of different enough faiths there is a greater difference in priories and whom you serve. That can often tear a relationship apart.
Even if you are of the same religion, make sure you guys are on close enough pages to bring each other closer together in life. Personally my husband and I are Christians, but we had to dive further. There are so many little and big variances in Christianity that finding someone who is compatible can be difficult even in the same church.
So if you do find yourself with more religious differences than you'd like, perserverre. Rely on the values that you share and come to a middle ground. If need be, make agreements and compromises. Value your relationship and faith together. Stay strong and full of love. Respect one another in whatever choice of religion they make.