When it comes to God’s sexual ethic, there’s a clear rationale for what’s commanded. His Word doesn’t so much show us a theology of sexuality or sexual ethics as it does a theology of marriage. Human marriage, we see repeatedly, is to point us to the ultimate marriage between Jesus and his bride, the church. It’s a signpost to the big thing God is doing in the universe—drawing together a people to belong to his Son. That vision explains the contours and boundaries we see in Scripture’s teaching about marriage. Once we unpack it we see why God insists that sex is for marriage (since only in a covenantal relationship with him do we have the ability to be vulnerable and intimate); that marriage is between one man and one woman (since God brings together two unlike yet complementary beings in a union); and why Christians are to marry only those in the faith (since our union with Christ means we cannot painlessly unite with someone who doesn’t also belong to him).