CCC 1631 This is the reason why the Church normally requires that the faithful contract marriage according to the ecclesiastical form. Several reasons converge to explain this requirement:1
– Sacramental marriage is a liturgical act. It is therefore appropriate that it should be celebrated in the public liturgy of the Church;
– Marriage introduces one into an ecclesial order, and creates rights and duties in the Church between the spouses and towards their children;
– Since marriage is a state of life in the Church, certainty about it is necessary (hence the obligation to have witnesses);
– The public character of the consent protects the “I do” once given and helps the spouses remain faithful to it.
1 Cf. Council of Trent: DS 1813-1816; CIC, can. 1108.