What does it mean to be married? There are two lenses through which this question can be answered. There's legal marriage as recognized by our government. Then, there's spiritual marriage as recognized by the church, or "god."
It is unfortunate that the word "marriage" is used for both religious and legal unions. As the current conflict over whom should be allowed to marry whom is a failure to separate church and state.
From a monotheistic religious viewpoint, the government does not define the parameters of marriage. Instituted by "god" through "sacred" texts, the institution of marriage is the ownership of a woman transferred from her father to her new husband. (Discussed in Marriage Manifesto, Part I: A Biblical History.)
The New Testament updates this a little bit, stating that the husband's and wife's bodies belong to each other (1 Corinthians 7). Still a far cry from personal civil rights. In more recent history, though, Christian marriage is one man with one woman.
What's important here is that America's Religious Right sees marriage as validated by "god" and not by earthly authorities. This is why gay marriage will never be acceptable. The Bible says that "men who practice homosexuality" (1 Corinthians 6) have "committed an abomination" (Leviticus 20). They will not "inherit the kingdom of God" (1 Corinthians 6). I guess this is supposed to be some kind of threat? Anyway, I digress.
The Religious Right cannot accept gay marriage because it is not compatible with "god's" words in the Bible. Sadly, it is not the recognition of a spiritual marriage that the homosexual community is seeking. (At least as I understand it. Please correct me if I'm wrong.) All these queers want is to visit their partners in the fucking hospital and receive health care benefits for fuck's sake. These are legal issues, and not a place where the church should be sticking it's nose.
A legal marriage is a union between to individuals that is recognized by the state. This is a union mutually agreed upon (hopefully) by two adults. In the eyes of the law, the two individuals are considered to be bound together in the same way that biological family members are tied together. Married individuals are the closest kin a person can have.
Those who are legally married have rights that unmarried folks don't have. Like visitation rights in jail or the hospital, legal guardianship of children, and benefits offered through employers. Does "god" really object to who visits a dying man? Would "god" care if a same-sex parent signed a field trip permission slip? Is "god" really offended when Lipstick gets her cavity filled using her partner's insurance?
Legal marriage is about choosing your family, selecting who is financially, functionally, and personally responsible for you and to you. Bible Thumpers will never abdicate the definition of "marriage." So, maybe it's time to reify legal unions with a term that isn't dripping with doctrine. Part III will address where we go from here.