Bishop John Chane points out that the Christian understanding of marriage has undergone extensive changes in the past 2000 years in an opinion published on the Washington Post site.
After detailing the developments and pointing out that the issue is not settled for many right now, he goes on to critique the reactions of some churches to the D.C. Council's decision to recognize same-sex marriages by pointing out that the action explicitly recognizes a right to disagree.
Bishop Chane writes, in part:
"Most media coverage of the D.C. Council's steps toward civil marriage equality for same-sex couples has followed a worn-out script that gives the role of speaking for God to clergy who are opposed to equality. As the bishop of the Episcopal Diocese of Washington, I would say respectfully to my fellow Christians that people who deny others the blessings they claim for themselves should not assume they speak for the Almighty. And to journalists I would offer a short history of changing Christian understandings of the institution of marriage.
[...]Our evolving understanding of what marriage is leads, of necessity, to a re-examination of who it is for. Most Christian denominations no longer teach that all sex acts must be open to the possibility of procreation, and therefore contraception is permitted. Nor do they hold that infertility precludes marriage. The church has deepened its understanding of the way in which faithful couples experience and embody the love of the creator for creation. In so doing, it has put itself in a position to consider whether same-sex couples should be allowed to marry.
Theologically, therefore, Christian support for same-sex marriage is not a dramatic break with tradition, but a recognition that the church's understanding of marriage has changed dramatically over 2,000 years. "
Read the full essay here.