Follow me on this one for a second. Within the Christian tradition, I think its fairly uncontroversial that Jesus Christ is the archetype, the ultimate definition, the mesoform of what it means to be human. I suppose this could be disputed, but within Christian theology this is pretty axiomatic. Jesus’s own historical, contingent, particular human life defines what it means to be human in a way that is more significant than any other determinate factor of human existence.
If this is true, what implications might this have for a theology of marriage and sexuality? In CD III/4 Barth unfortunately defines humanness by sexual differentiation, thereby taking an Adamic definition for humanity rather than approaching the issue Christologically (see p. 158ff for example). In so doing, Barth makes sex and marriage the definition, or at least the full expression of the meaning of humanity. However, this is a decidedly non-Christological approach.
If we take Christology as our starting point, recognizing that (unless Dan Brown turns out to be right) Jesus was unmarried, not sexually active, and produced no children, we come to some very different conclusions. If the One who, in his life, crucifixion, and resurrection defined and actualized for us the very definition of humanness, what does that say about humanness? Clearly it says that marriage, sexual activity, and bearing children do not have any central place in the definition thereof.
Let us be absolutely clear on this point. If Christ is truly the fullness and definition of authentic humanity, we must say categorically that marriage, sex, and parenthood tell us nothing whatsoever of ultimate significance about humanness. If marriage, sex, and parenthood are somehow the fullness of humanity we are forced to say that Christ, far from being the true human as the Christian tradition proclaims, was in fact, sub-human. To grant sexuality any sort of ultimacy with respect to the definition of humanness is to deny that Jesus is the true human being.
So, if we take a Christological defintion for the meaning of humanness, sexuality by definition tells us absolutely nothing about the ultimate meaning of humanness. It may, through the gracious operation of the Holy Spirit be comandeered and become in many and sundry ways a parable of the kingdom, just as many of the trivial aspects of human life are open to God’s interruption and transfiguration. But, insofar as the meaning of authentic human existence, sexuality tells us nothing. Not if we really believe that Jesus defines for us what it means to be be human. And, further to this point, only when we allow sex to be truly and wonderfully insignificant, to be trivial, will it be able to be recived as a gift rather than gulpingly grasped in an idolatrous fit of fetishizing.