The New International Version of the Bible consistently translates the Greek word “σαρκος” as “sinful nature” in contexts where it refers to that part of a person that tends toward sin. Older translations had it as “flesh,” and I think something is lost in the newer rendering, namely, the connection with the body. Indeed, it seems that this connection is the very one that the translators sought to sever in changing the translation from “flesh” to “sinful nature.”
God has no body. He is spirit and is not limited by physical form. He created people as an amalgam of body and spirit. We are not merely physical nor pure spirit. God created animals that have no spirit though they live and move as we do and even exhibit certain kinds of intelligence like our own. He also created angels, which are pure spirit and have no bodies. People alone of all his creation (so far as we know) are made of body and spirit combined. Not until God had created people did he declare his creation “very good,” and Christian tradition has held that both body and spirit are good. God spoke all things into existence by the power of his word. But when he created people, he got his hands dirty (Gen 2:7). So God took a very personal interest in the making of people and made them just as he wanted them.
Nevertheless, when the New Testament writers write about the active principle within us that causes us to tend toward sin, they called it “the flesh.” They recognized that sin arises from appetites and desires, and that our desires come from our own flesh. We all experience desires: hunger, thirst, sexual desire, the desire for comfort and security. All these desires have a wholesome and appropriate expression. But the body seems to know nothing of what is wholesome or appropriate. A plate of cookies may tempt me no matter how many calories I’ve had recently. If I yield, I risk gluttony. In the same way every evil desire arises from the flesh: lust, greed, hatred, envy, conceit—each clamors to be fulfilled at whatever expense to our well-being and integrity.
The reason for this state of affairs seems to be that our bodies are not yet redeemed. God has given life to our spirits, but our bodies remain the same old bodies we always had. They will not be redeemed until the resurrection. Thus Paul writes that “we ourselves, who have the firstfruits of the Spirit, groan inwardly as we wait eagerly for our adoption as sons, the redemption of our bodies. For in this hope we were saved. (Rom 8:23-24a)” He makes it clear that our great hope is to be free at last—not of our bodies, for then we would be but half-redeemed—but of our flesh. While we live in the body, we are still subject to the desires of the flesh. We must put to death the flesh by the Spirit of God. This does not mean, as some have supposed, that we mutilate our bodies or practice some kind of self-torture. It means that we are to oppose the desires of the flesh by yielding to the guidance of the Spirit. “Mortifying the flesh” means saying no to its evil desires; it means developing the habit of saying no so that the flesh grows weak and dies.
Christians often contribute to the mind–body split by saying that when you die you go to heaven, and that’s that. But heaven is not our destination. The Bible clearly tells of a resurrection of the body, when those who have been redeemed get new, incorruptible bodies, free at last of the sinful nature that dogs us now. It tells of a time yet to come when God re-makes the world and the city of God comes down to earth and he makes his dwelling with us. We will go to him when we die but only so we can return with him when he comes to reign. Our destiny is to be united, body and spirit, for all eternity as God intended from the beginning.