My son is Catholic and woman he will marry is Lutheran. Her father is a minister and will be doing the ceremony. May a Catholic priest be present to bless the marriage? What is the rule?
The Church requires that Catholics marry Catholics, and that they do so within a Catholic ceremony. Marriage, as a sacrament, is strengthened by the faith of the parties, and since marriage is ordered toward the good of the spouses and the procreation of children, it is only logical that the good of the spouses is strengthened by a common faith, by regular reception of the sacraments together, by common prayer, and by a common identity.
Even more, the Church knows that children’s faith is best secured when both parents share that faith.
That said, the Church recognizes that human heart and affections are difficult to regulate.
Understanding that there are circumstances where a Catholic might desire to marry someone of another faith, and respecting the autonomy of the individual, the Church can grant permission for a Catholic to marry a baptized non-Catholic, or even a dispensation for a Catholic to marry an unbaptized person. In both cases, before the permission or dispensation is granted, some assurances are required: the Catholic party needs to be advised of the seriousness of this exception, he has to state that he is intending to continue to practice his Catholic faith, and he has to state that he will do all within his power to ensure that the children born to the marriage will be brought up in the faith. In addition, the non-Catholic party must be advised that the Catholic party has made these promises. Then, if the bishop is convinced that this marriage will not be a danger to the faith of the Catholic party, then he may give his permission, or grant a dispensation.
The bishop has the further authority, should he deems it reasonable to do so, to grant a dispensation from canonical form, that is, permission for the Catholic to be married by a non-Catholic minister.
If that dispensation is given, then the wedding should follow whatever format the non-Catholic minister uses. It’s not good to “mix” rituals and have a Catholic priest do part and a (in this case) Lutheran minister do part. Particularly egregious (and actually invalid) are situations where the Lutheran minister receives the vow of the Lutheran party and the Catholic priest receives the vows of the Catholic party. There must be only one minister officiating.
Priests are not forbidden to attend such weddings, and may do so as a guest, especially if there’s a close family relationship. Priests may, with their bishop’s permission, even attend “in choir” (that is, they may wear their proper choir dress). I suppose it would not be entirely wrong for such a priest to have some small part of the ceremony, such as proclamation of the Gospel, the offering of a prayer, if his bishop permits it. One must allow the bishop to lead his diocese in the arena of ecumenism to avoid scandal or indifferentism (cf. art. 157 of the Directory on the Principles and Norms of Ecumenism).
If the bishop does not give his permission, or if the priest or deacon prefers (I’d probably opt for this option), the priest can skip the wedding ceremony that’s taking place with a dispensation from form, and instead, come to the wedding reception and give the newlywed couple a blessing and bless the food.
Even better, Father could greet the couple after Mass on the Sunday after the wedding (just because one gets married on Saturday, doesn’t give one permission to skip Mass the next day!. Have Gaius and Sempronia come up to the Communion rail and give them a blessing before they toddle off to their honeymoon destination and their lifelong, happy marriage together.