"There is no deadlier weapon than the will! The sharpest sword is not equal to it! There is no robber so dangerous as Nature...yet it is not nature that does the damage: It is man's own will." Chuang Tzu
Sin is, at its essence, a corruption of the will. The orthodox Christian position is that our desire is flawed, not our bodies. Sin is a matter of software, not hardware. Our flawed desire takes the form of that "blind self-love" that Calvin describes, or the pride that Augustine condemns. Whenever love of self is placed above love of God and neighbor--we sin. That is at the heart of what Paul speaks about when he describes sin as living kata sarka, or "in the flesh." (Romans 8:5) We orient ourselves towards our own physical desires, and allow our own needs to rule over the needs of others.
That can't be understood to mean that the fulfillment of physical needs itself is evil. It isn't wrong to be hungry, or to eat. But the Ultimate Colossal Burger at Ruby Tuesday's has more calories than most sub-Saharan-Africans get in a day...and that's before your side of fries and half-gallon of soda.
It isn't wrong to feel sexual desire. Sharing that intimacy with a partner is good, and the potential for the creation of new life is a blessing. But when other human beings become just a means to our own pleasure, and all we think about all day is bangbangbangbangbang, then we live not according to our physicen kresin, our "natural functions" (Romans 1:17), but according to sin.
So now I'll weave this thread into my prior musings--where does this leave us relative to homosexuality? The condemnations of the "homosexual lifestyle choice" that arise from many Christian leaders have at their heart this understanding of sin as a flaw of the will. That's why the emphasis on homosexuality as a choice must be vigorously repeated and defended. This, of course, flies in the face of what science and our God-given ability to examine our world shows us-but so what?
Common sense on sexual identity seems to have a sharper edge here. Take me, for instance. I'm a heterosexual male. I have always been attracted to women. Sometimes--sophomore and junior years in high school come to mind--that attraction has been so intense as to be almost a form of madness.
I could no more choose to be attracted to another man than I could choose to be a duck. It isn't how God made me. If you're similarly heterosexual--ask yourself the same question. Could you make that choice? Didn't think so. Choice, volition, and will have nothing to do with orientation itself.
If that is so, then how is homosexuality itself a sin?