This is not to say that marriage was condemned outright by more than a few, but neither was it particularly praised. It helped prevent sins like fornication, but there was little good about it in and of itself since it still bore the taint of sexuality. Marriage for procreation was not a bad thing, but marital celibacy was better, and remaining celibate and unmarried was best. As time went on, the religious view of marriage improved. It still wasn’t regarded as particularly holy, but nor did theological writers see it as a step up from sin.
Significant change in attitudes towards marriage began to come about in the 12th century. Greater attention to what people believed and brought made the question of marriage into a bone of contention. Several heretical groups, most notably the Cathars, considered marriage an out and out sin. Catholic writers, meanwhile, chose to defend marriage as something positive. Writers like Gratian and Hildegard of Bingen listed the moral and personal benefits of marriage. They viewed sexuality within marriage as a good thing, with Gratian even going so far as to say that consummation was what made a marriage a sacrament and therefore impossible to end. Not everyone agreed with the sacramental idea of marriage, but the idea was gaining force.
Within a century, argument on the subject was minimal, though the official declaration that marriage should be regarded as a sacrament wouldn’t come until the Council of Trent in the 16th century. This, once again, may have had something to do with disagreement from other religious groups. Reformation leaders like Luther and Calvin rejected the sacramental idea of marriage, viewing it rather as a product of the natural order, not something religious. Over the course of centuries, marriage had gone from something one step up from sin, to sacred on the one hand and completely natural on the other.
*St. Paul’s oft quoted “It is better to marry than to burn” (1 Corinthians 7:9) comes to mind. Not the most stunning endorsement of marriage.
Brundage, James A. Law, Sex, and Christian Society in Medieval Europe. Chicago: University of Chicago Press, 1987.
"Canons on the Sacrament of Matrimony," Council of Trent - ETWN.com
Marriage Canons in The Decretum of Gratian - Catholic University of America
Sacrament of Marriage - Catholic Encyclopedia