How can the priest be the minister of the Sacrament of Matrimony in Eastern Catholic and Eastern Orthodox weddings, but not in Roman Catholic and Protestant weddings?
I do not think you need a priest in the Catholic Church to celebrate the Sacrament of Marriage. A deacon can preside over a Catholic wedding. In the Eastern Churches a priest must be there to celebrate the Sacrament. However this is the Catholic wedding couple usually ask for a priest to celebrate the marriage. I don’t know exactly why there is these differences in both East and West but I will give it a try. I believe the ministers of the Sacrament in a Catholic wedding is the man and woman who marries. The priest or someone else just acts as a witness. The minister of the Sacrament in the East is the priest and not the couple. I think this is the major difference of how the East and West looks at the Sacrament of marriage. The difference is in who is the minister for the Sacrament. The Catholic Church only needs the vows of the couple to enact the marriage. The Eastern Church needs the priest as the couple are not seen as the ministers of the Sacrament.
In both east and west the marriage requires the Church approved form of celebration, the couple, and two witnesses. The approved form of celebration in the eastern churches requires a priest, and neither a deacon nor layman, must bless the marriage in the eastern Catholic churches for *validity, *except in extraordinary situations. Even in extraordinary situations, the couple is not to neglect getting the blessing later.
**CCEO (eastern Catholic canon law) **
If one cannot have present or have access to a priest who is competent according to the norm of law without grave inconvenience, those intending to celebrate a true marriage can validly and licitly celebrate it before witnesses alone:
INDENT in danger of death;
(2) outside the danger of death, as long as it is prudently foreseen that such circumstances will continue for a month.
In either case, if another priest, even a non-Catholic one, is able to be present, inasmuch as it is possible he is to be called so that he can bless the marriage, without prejudice for the validity of a marriage in the presence only of the witnesses.
If a marriage was celebrated in the presence only of witnesses, the spouses shall not neglect to receive the blessing of the marriage from a priest as soon as possible.