Catechism number 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:¹³²
- 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.