Over at Spiritual Friendship, my friend Kyle Keating has written this post on the theology of St. Athanasius, 4th-century bishop of Alexandria and chief opponent of the heretic Arius. The gist: our framework for morality must be grounded in the overall storyline of Scripture. If we hold to any ethic—and in this case any ethic departing from the traditional view of marriage and sexuality—which does violence to the biblical narrative, then we cannot properly call it a Christian ethic.
As with Kyle, I find a much more persuasive case can be made for the traditional view of sexuality based on Genesis 1-3 than on any of the so-called “clobber passages” (Lev. 18:22; 1 Cor. 6:9; etc.). But beyond grounding our view of marriage in creation (which in itself is very convincing, IMO), Kyle goes on to ground it in the biblical picture of the church as the bride of Christ. To be sure, there is a unity between Christ and his bride, since Christ actually took on human flesh to purchase our redemption. But there is also a fundamental distinction, due to the infinite chasm of being between the Creator and the creature. Therefore, to advocate same-sex marriage is in essence a blurring of the distinction between Creator and creature.