The Catechism in Questions & Answers

742. What significance does the Christian faith have for the success of the marriage?

It is desirable for spouses to have a common agreement in matters of faith, however, the fact that both partners are Christians is no guarantee for a harmonious matrimony.
All questions pertaining to their life together should be discussed and clarified before marriage, particularly in the case where either one of the partners is of a different culture, religion, or confession.