Tradition does not come from nothing. It distills the experience and wisdom of generation upon generation of human lives.
The first man and woman lived their life in a natural way. They first behaved in instinctive ways and modified their behavior based on the results of their actions until they assembled a coherent way of living. Their children imitated their way of living, as children do, and tweaked some parts based on results. Bit by bit, generation after generation, on it went, building a tradition. From these family traditions grew traditions of clan, tribe, nation, and civilization. Traditions have the weight of the past in them. They are human ways of surviving that have been proved to work over hundreds and thousands of years.
Historians and anthropologists tell us that our kind of monogamous marriage is a relatively recent development. Earlier peoples tried many other forms of marriage: polygamous; polyandrous; monogamous and monoandrous; matrilocal; patrilocal; matrilineal; patrilineal; both patrilineal and matrilineal simultaneously; group and ladder arrangements; even matrilocal and matrilineal non-marriage in which women couple freely with any men who please them, raising their children in their own mother's home (or village) with their brothers serving as adult male role models for the children and men left without domestic responsibilities. The Western tradition settled on monogamy (or one man marrying one woman for life) for historical reasons, and stayed with it because it is kinder to women and children than other family forms, because its inherent stability allows wealth to accumulate, because it allows all the men in society to marry thus bringing peace to society, and because children have a better chance of living to adulthood in monogamous families.
I can hear some of my readers complain. "But this isn't marriage. Marriage is true love. It is companionship. It is a commitment to remain eternally infatuated with one person, until it ends." My counterargument is that marriage as a family form is important. It has to do with the way that people reproduce and accomplish long-term goals that take more than a lifetime. "Be fruitful and multiply," is not only God's command, it is the central fact of all life, including human life. Reproduction is our purpose as living beings, if you will. Certainly if we do not reproduce then we will be no more than a footnote in a hundred years.
Compare the concept of marriage as a family form, the structure in which humans reproduce, to the concept of marriage as sexual companionship. One continues our kind. The other gratifies libido and provides pleasure. One has long-term effects and encourages the accumulation of wealth and technological progress. The other is basically short-term and encourages spending. While exceptions happen, the structure of the two types of marriage necessarily produce quite different effects.
From looking at marriage in the anthropological way to looking at marriage in the romanticized 20th century way as sold by Hollywood is a leap from marriage as a family form to marriage as an expression of true love between two "adults," with children as an afterthought or even a distraction from its purpose. The two kinds of marriage are not the same. We could say marriage is family. Or we could say marriage is companionship and eternal infatuation. But when we say both we confuse the issue and render the word "marriage" meaningless.
With regard to infatuation, is a lustful gaze across the dance floor at the senior prom the foundation of a lifetime together? I'm convinced that marriage as an expression of true love between two people is an adolescent parody of real marriage, which holds family as its purpose. Our modern society has extended childhood into the teen years, pushing back the onset of adulthood from puberty, where it used to be reckoned, to the age of 21 when it's now legal to get drunk. With the invention of adolescence, society has transformed many formerly adult things into adolescent versions. Perhaps the most important of these is marriage.
I believe that changing the popular definition of marriage from the core of a new family and the intersection of two extended families was a big mistake. It has driven down the rate of reproduction in the West to the point where populations are dying off and our Ponzi scheme social security funds are poised to fail, while our sparse population is attracting hungry migrants from more crowded parts of the world. And it has damaged us: our behavior, our ability to plan for the long term, our moral clarity.
It's time to change the definition back. Marriage should mean family; a new family and the joining of two extended families. Marriages without children are sad and incomplete and deserve our sympathy and kindness. They are not the model which families blessed with children should emulate. Families with children, parents, grandparents, aunts and uncles and cousins, are the model.