Historically, marriage was to assure the ligitimacy of a man's off-spring... one source says "...The best available evidence suggests that it’s (marriage) about 4,350 years old. For thousands of years before that, most anthropologists believe, families consisted of loosely organized groups of as many as 30 people, with several male leaders, multiple women shared by them, and children. As hunter-gatherers settled down into agrarian civilizations, society had a need for more stable arrangements. The first recorded evidence of marriage ceremonies uniting one woman and one man dates from about 2350 B.C., in Mesopotamia. Over the next several hundred years, marriage evolved into a widespread institution embraced by the ancient Hebrews, Greeks, and Romans. But back then, marriage had little to do with love or with religion.
Marriage’s primary purpose was to bind women to men, and thus guarantee that a man’s children were truly his biological heirs. Through marriage, a woman became a man’s property. In the betrothal ceremony of ancient Greece, a father would hand over his daughter with these words: “I pledge my daughter for the purpose of producing legitimate offspring.”
This source continues "... By the eighth century, marriage was widely accepted in the Catholic church as a sacrament, or a ceremony to bestow God’s grace. At the Council of Trent in 1563, the sacramental nature of marriage was written into canon law.
The Church's blessings did improve the lot of wives. Men were taught to show greater respect for their wives, and forbidden from divorcing them. Christian doctrine declared that “the twain shall be one flesh,” giving husband and wife exclusive access to each other’s body. This put new pressure on men to remain sexually faithful." (Source: The Week's Magazine)