The Catechism of the Catholic Church (no. 1633) insists on the difficulties which can arise in the case of mixed marriages (between a Catholic and a baptized non-Catholic), and even more so when there is disparity of cult (a marriage between a Catholic and a non-baptized person). The Catechism goes on (1634): "Differences about faith and the very notion of marriage, but also different religious mentalities, can become sources of tension in marriage, especially as regards the education of children. The temptation to religious indifference can then arise" - especially among the children, who will have to grow up in a secularized world without the support that comes from a home united in faith.
Disparity of cult being a canonical impediment (c. 1086), such a marriage cannot be validly contracted without a dispensation. This is not granted unless the Catholic party is ready to protect his or her own faith, and sincerely promises to do all in their power to have the children baptized and educated as Catholics (cf. cc. 1124-25).
The Catechism notes that the Catholic spouse has a particular task - to work so that "the free conversion of the other spouse to the Christian faith" may come about. It adds: "Sincere married love, the humble and patient practice of the family virtues, and perseverance in prayer can prepare the non-believing spouse to accept the grace of conversion" (1637). It is logical that the Catholic spouse, while fully respecting the conscientious freedom of their partner, should work for this. Love makes a person want whatever is good for the loved one; and few gifts are better than the grace of freely embracing the Catholic faith.