Movements are renewed by continually returning to their Biblical heritage in innovative ways. They die when innovation betrays that heritage.
Andrew Walker has written the best response to the same sex marriage debate that I’ve read.
Whatever one feels about organized religion or Christianity writ large, Jesus remains a highly favored cultural icon of compassion, charity, and love. Even most atheists and avowed non-Christians will acknowledge that Jesus is someone worth admiring and imitating.
Because of his enduring attraction, Jesus is continually summoned to support causes, regardless of how rooted those causes are in the words and deeds of Jesus himself. So there’s “Take Back America for God” Jesus; pro-universal healthcare Jesus; free market Jesus. With the ascendancy of same-sex marriage, a recent and popular incarnation is the pro-same-sex marriage Jesus. Proponents of same-sex marriage have wisely attached their cause to the Son of God.