As far as I know, Amoris Laetitia is the first magisterial document of the Holy See to decide a certain question concerning baptism and marriage:
75. In the Church’s Latin tradition, the ministers of the sacrament of marriage are the man and the woman who marry; by manifesting their consent and expressing it physically, they receive a great gift. Their consent and their bodily union are the divinely appointed means whereby they become “one flesh”. By their baptismal consecration, they were enabled to join in marriage as the Lord’s ministers and thus to respond to God’s call. Hence, when two non-Christian spouses receive baptism, they need not renew their marriage vows; they need simply not reject them, since by the reception of baptism their union automatically becomes sacramental. Canon Law also recognizes the validity of certain unions celebrated without the presence of an ordained minister. The natural order has been so imbued with the redemptive grace of Jesus that “a valid matrimonial contract cannot exist between the baptized without it being by that fact a sacrament”. The Church can require that the wedding be celebrated publicly, with the presence of witnesses and other conditions that have varied over the course of time, but this does not detract from the fact that the couple who marry are the ministers of the sacrament. Nor does it affect the centrality of the consent given by the man and the woman, which of itself establishes the sacramental bond. This having been said, there is a need for further reflection on God’s action in the marriage rite; this is clearly manifested in the Oriental Churches through the importance of the blessing that the couple receive as a sign of the gift of the Spirit.
Previously, this question was, to the best of my knowledge and understanding unsettled by the Magisterium. In Amoris Laetitia, Pope Francis settles the question in favor of automatic marriage in a certain type of case, specifically:
1. Two unbaptized persons
2. who have a valid natural marriage (one man and one woman)
3. who both convert to Christianity
4. and are baptized
But he also correctly states that “The Church can require that the wedding be celebrated publicly, with the presence of witnesses and other conditions that have varied over the course of time….” Currently, no such requirements exist in the Latin Rite. But the Eastern Rite (Oriental Churches) does require a priest to bless the marriage for a valid Sacrament.
In either Rite, a couple in such a situation has a valid marriage from the time of their baptism. But they should consult with their pastor and bishop, since a valid marriage is usually recorded in parish records at the parish of their baptism, or in diocesan records. An Eastern Rite bishop might require such a couple to meet with a priest for the blessing required by the Canon Law of the East. In the Latin Rite, such a couple would still be well-advised to find out if the bishop of their diocese requires them to meet with a priest, so that the diocese may determine that the marriage is valid under the above stated doctrine.
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