Many argue that marriage is essentially and necessarily a religious rite — they conceive of marriage in almost exclusively religious terms. Therefore, legalizing gay marriage constitutes a type of sacrilege and an unjustified intrusion of the state into what is necessarily a religious matter. Because of religion's traditional role in sanctifying marriages and presiding over wedding ceremonies this is understandable, but it's also incorrect.
The nature of marriage has varied greatly from one era to the next and from one society to the next. In fact, the nature of marriage has varied so much that it is difficult to come up with any one definition of marriage which adequately covers every permutation of the institution in every society which has thus far been studied. This variety alone ensures the falsehood of the claim that marriage is necessarily religious, but even if we focus exclusively on the West — or even exclusively on America — we still find that religion has not been regarded as a necessary component.
Marriage in Early America
In her book Public Vows: A History of Marriage and the Nation, Nancy F. Cott explains at length how deeply intertwined marriage and public government have been in America. From the beginning marriage has been treated not as a religious institution, but as a private contract with public implications:
Although the details of marital practice varied widely among Revolutionary-era Americans, there was a broadly shared understanding of the essentials of the institution. The most important was the unity of husband and wife. The "sublime and refined...principle of union" joining the two was the "most important consequence of marriage," according to James Wilson, a preeminent statesman and legal philosopher.
The consent of both was also essential. "The agreement of both parties, the essence of every rational contract, is indispensably required," Wilson said in lectures delivered in 1792. He saw mutual consent as the hallmark of marriage — more basic than cohabitation.
Everyone spoke of the marriage contract. Yet as a contract it was unique, for the parties did not set their own terms. The man and woman consented to marry, but public authorities set the terms of the marriage, so that it brought predictable rewards and duties. Once the union was formed, its obligations were fixed in common law. Husband and wife each assumed a new legal status as well as a new status in their community. That means neither could break the terms set without offending the larger community, the law, and the state, as much as offending the partner.
Early Americans' understanding of marriage was closely tied to their understanding of the state: both were seen as institutions which free individuals entered into voluntarily and thus could also exit voluntarily. The basis of marriage was not religion, but the wishes of free, consenting adults.
Marriage in Modern America
The public character of marriage which Cott describes also continues today. Jonathan Rauch, in his book Gay Marriage, argues that marriage is much more than just a private contract:
[M]arriage is not merely a contract between two people. It is a contract between two people and their community. When two people approach the altar or the bench to marry, they approach not only the presiding official but all of society. They enter into a compact not just with each other but with the world, and that compact says: "We, the two of us, pledge to make a home together, care for one another, and, perhaps, raise children together.
In exchange for the caregiving commitment we are making, you, our community, will recognize us not only as individuals but as a bonded pair, a family, granting us a special autonomy and a special status which only marriage conveys. We, the couple, will support one another. You, society, will support us. You expect us to be there for each other and will help us meet those expectations. We will do our best, until death do us part.
In debates over gay marriage, much attention is paid to legal rights which same-sex couples miss out on because of their inability to marry. If we take a close look at those rights, however, we find that most are about helping couples care for each other. Individually, the rights help spouses support each other; taken together, they help society express the importance of being a spouse and the fact that marrying changes who you are and your status in the community.
Marriage in America is indeed a contract — a contract that comes with more obligations than rights. Marriage is a civil right that is not now and has never been dependent upon any one religion or even religion in general for its justification, existence, or perpetuation. Marriage exists because people desire it and the community, working through the government, helps ensure that married couples are able to do what they need to in order to survive. At no point is religion needed or necessarily relevant.