Many argue that marriage is essentially and necessarily a religious rite. These Christians conceive of marriage in almost exclusively religious terms and conclude that therefore legalizing gay marriage constitutes a type of sacrilege — 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 by everyone at all times.
There is nothing wrong with individuals or churches treating marriage as sacred or sacramental, but this is not a debate about what individuals or private institutions should be doing. No one has even tried to argue that a church can’t or shouldn’t treat marriage as sacred. This is a debate about how the government should treat people and how civil laws on marriage should be written.
Is there any obligation on the part of the government to define civil marriages in a manner that does not conflict with religious conceptions of the same? Is there any obligation on the part of government to define civil marriage in manner that establishes, recognizes, supports, or endorsees any religious conception of marriage as “sacred”? Of course not. It doesn’t matter what religious believers think about marriage, nor does it matter how important a particular definition of marriage happens to be within their religious system. The government is separate from and independent of their religion and must define marriage in a manner consistent with the secular principles upon which the government and the laws are founded.