"Both opposite-sex and same-sex love are used, in the Bible, as images of God's love. The opposite-sex love is found in marriage—sexually exclusive marriage, an image which recurs not only in the Song of Songs but in the prophets and in the New Testament—and the same-sex love is friendship. Both of these forms of love are considered real and beautiful; neither is better than the other. But they're not interchangeable. Moreover, Genesis names sexual difference as the only difference which was present in Eden. There were no racial differences, no age difference, no children and therefore no parents. Regardless of how literally you want to take the creation narratives, the Bible sets apart sexual difference as a uniquely profound form of difference. Marriage, as the union of man and woman, represents communion with the Other in a way which makes it an especially powerful image of the way we can commune with the God who remains Other. That's a quick and dirty summary, but it seems to me more responsive to the texts, more willing to defer to historical Christian witness, and more attuned to the importance and meaning of our bodies than most of the defenses I've read of Christian gay marriage."