Marriage's traditional cultural function has been to manage property and make arrangements for the children, and spell out the rights and obligations of all parties involved. Different cultures manage it in different ways, some have dowries, some demand a bride-price, divorce may or may not exist and there are many other details which vary from culture to culture. There is the basic biological imperative, to reproduce as much as possible, but it must be amended because we are social animals who have developed complex communities of many different types. So marriage isn't just about sex and babies any more.

The church seems to be mainly obsessed with managing sex--we are creatures biologically evolved to be pregnant by the time we have reached puberty, but any social structure above the Paleolithic demands additional embellishments to ensure social continuity, community cohesion, separation and specialization of labor and orderly inheritance. As for the importance of sex and reproduction, remember, that most cultures allow for remarriage because death was so common among the young during most of our history. Today, among the aged, its mostly about companionship and friendship; in the past, it was survival of the young. Someone had to take care of the youngsters if a parent died, and fertile adults could not be wasted if their mate passed.

I live in a retirement community where there are a large number of widows and widowers, but there is also quite a bit of remarriage (and even some good old=fashioned shacking up!). People not only get lonely, they need partners just to survive. We can't move in with our kids any more when we get too old to hunt, or farm, and pay for our keep by babysitting and teaching the grandchildren while their parents go into the bush to forage.

Marriage systems are not created by god, they are cultural institutions that evolve to meet different conditions. Those that don't serve their communities are selected against, and either change, or their cultures fail. Marriage custom takes on many forms today, but they all have one thing in common, they served their cultures well enough to have survived to this day, not by how how well they served the bride and groom, but by how well they served the community as a whole.

When technology or social change alters conditions, marriage has to change too or society is doomed. We have different marriage institutions than did our hunter-gatherer ancestors, our slash-and-burn forebears, our earliest farming civilizations, and now going into our industrial and post-industrial age. Insisting on cultural norms that worked well in the past is a recipe for disaster.

Even the extended family, which was still relatively common among my friends and relatives when I was growing up, has becoming increasingly rare. Today, even the traditional nuclear family is rapidly becoming obsolete in a world dominated by geographic separation and economic mobility and change. We don't have more divorce now because of a decline in morality, we have it because there is little cultural pressure to maintain families intact, and because there is more economic opportunity to allow changing mates. We have developed economic and legal arrangements that make divorce, remarriage and single-parent families possible. If your marriage is bad, because, say, your husband is a murderous brute, you can dump the sonofabitch.

The church's role in codifying and preserving these cultural arrangements may have been essential in the past, but nowadays, it just doesn't cut it anymore.