The Sacrament of Marriage

A medieval marriage, from a British Library ms.

The Christian churches that have survived until the modern era (Roman Catholicism, Eastern Orthodoxy, Oriental Orthodoxy) consider marriage a sacrament; that is, one of the seven

efficacious signs of grace, instituted by Christ and entrusted to the Church, by which divine life is dispensed to us. The visible rites by which the sacraments are celebrated signify and make present the graces proper to each sacrament. [Catechism of the Catholic Church]

Not everyone saw it that way. A Christian movement that was declared heretical, Catharism, had an entirely different view. (We call the movement "Catharism," but they called themselves Perfecti, "the perfected.") The Perfecti saw sexual reproduction as sinful, and wanted nothing to do with it. This meant they avoided anything that was the product of sexual reproduction, including animals that others would consume as food. They were opposed to marriage completely; so completely, that proof of legal marriage was enough to get a charge of heresy dismissed, if one was accused of being a Cathar.

It is due to the Cathars that marriage is considered a sacrament. The Synod of Verona in 1184 (during the pontificate of Pope Lucius III) was convened to discuss and condemn heresy. It declared marriage a sacrament in opposition to what was being said by Cathars and other heretical groups like the Waldensians.

This was despite the fact that marriage does not fulfill a goal in the same way as the other sacraments. There are sacraments of Christian initiation: Baptism, Confirmation, Communion. There are sacraments that "confer a character": Baptism, Confirmation, Holy Orders. Penance/Confession and Anointing of the Sick help to purify the soul. The sacrament of marriage puts a "stamp of approval" on the start of a new phase in a couple's lives and reminds them of their place in the community of Christians. In the words of one scholar:

Like the other sacraments, medieval writers argued, marriage was an instrument of sanctification, a channel of grace that caused God's gracious gifts and blessings to be poured upon humanity. Marriage sanctified the Christian couple by allowing them to comply with God's law for marriage and by providing them with an ideal model of marriage in Christ the bridegroom, who took the church as his bride and accorded it highest love, devotion, and sacrifice, even to the point of death. [source]

One of the most interesting aspects of marriage in the Catholic Church is that it relies on "free consent": two people choose to marry each other, and the Church only officiates, it does not give or deny approval to a marriage.