"The matrimonial covenant, by which a man and a woman establish between themselves a partnership of the whole of life, is by its nature ordered toward the good of the spouses and the procreation and education of offspring; this covenant between baptized persons has been raised by Christ the Lord to the dignity of a sacrament." (Catechism of the Catholic Church)
For Catholics, the Sacrament of Marriage, or Holy Matrimony, is a public sign that one gives oneself totally to this other person. It is also a public statement about God: the loving union of husband and wife speaks of family values and also God's values.
The parties to a marriage covenant are a baptized man and woman, free to contract marriage, who freely express their consent; "to be free" means:
- not being under constraint;
- not impeded by any natural or ecclesiastical law.
It is clear that while marriage, inasmuch as it is an outward sign of grace and also produces interior grace, has the nature common to all the sacraments, still, viewed as an external sign, it is unique and very different from the other sacraments. The external sign is a contract; hence marriage, even as an effective sign or sacrament, has precisely the nature and quality of a contract, its validity depending on the rules for the validity of contracts.
The marriage covenant, by which a man and a woman form with each other an intimate communion of life and love, has been founded and endowed with its own special laws by the Creator. By its very nature it is ordered to the good of the couple, as well as to the generation and education of children. Christ the Lord raised marriage between the baptized to the dignity of a sacrament.
Since marriage establishes the couple in a public state of life in the Church, it is fitting that its celebration be public, in the framework of a liturgical celebration, before the priest (or a witness authorized by the Church), the witnesses, and the assembly of the faithful.
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:
a. Sacramental marriage is a liturgical act. It is therefore appropriate that it should be celebrated in the public liturgy of the Church;
b. Marriage introduces one into an ecclesial order, and creates rights and duties in the Church between the spouses and towards their children;
c. Since marriage is a state of life in the Church, certainty about it is necessary (hence the obligation to have witnesses);
d. The public character of the consent protects the "I do" once given and helps the spouses remain faithful to it.
So that the "I do" of the spouses may be a free and responsible act and so that the marriage covenant may have solid and lasting human and Christian foundations, preparation for marriage is of prime importance.
(For more, cf: The Catholic Encyclopedia)