“It is probably not a coincidence that Christianity, and Christian notions of marriage, evolved in a largely peasant population,” writes Dustin Wax over at the group anthropology blog Savage Minds, which (from the point of view of us amateurs) provokes either fascination or a short nap.
“Marriage in such societies is generally not, as today’s formulation has it, a ‘relationship between a man and a woman,’ but a relationship between extended families in which the relationship between the particular people married is secondary at best--and often simply irrelevant. Thus, in many societies (such as the Biblical Hebrews), the practice of levirate (in which a man marries his brother’s widow) or sororate (in which a woman marries her sister’s widower) allow the kinship bond between families to remain unbroken regardless of the death of a spouse--structurally equivalent siblings become interchangeable in marriage because their function is identical.”
Hence arranged marriage, too, because the real purpose of marriage is to add to “social networks through which labor and trading can be arranged . . . . A large extended family might be allied by marriage with a dozen or more other extended families.” (Hmm, says I. That might be why, as recently as the early 1800s, I find three or four children in a single family of my ancestors marrying into the same other family.)
"It’s easy to see, then," Wax continues, "why marriage is so important in this kind of society. What is difficult is to understand what function it retains in a society such as ours (‘we’ here being post-industrial Westerners, especially urban Westerners) where labor and trade are organized through market, not kin, relations. Under the logic of industrial capitalism, marriage is not only unnecessary in many ways but can even be counter-productive.” All you veterans of commuter marraiges raise your hands. (There’s more, and the comments are good too.)
One more reason why you might expect the religious-minded to think twice before embracing the free market and all its works.