OUR FLESHLY NATURE

The thoughts of the corrupt mind are incapable of perceiving the things of God. All its desires, delights, cares, and fears are wrapped up in this present world, and are therefore fleshly. Just as the sun hides the heavens above it while revealing the things beneath, so carnal reason leaves the creature in the dark concerning spiritual truths, while enlightening his carnal knowledge most excellently. Every creature has its proper diet: the lion does not eat grass, nor the horse, flesh. Just so, what is food to the carnal heart, is poison to the gracious; and what is tasty to the gracious, is odious to the carnal.
Now according to this interpretation of flesh and blood, the apostle is not saying that the war is over between your old and new natures. You know from experience this is not the case. The Spirit lusts against the flesh and the flesh against the Spirit throughout the whole course of a Christian's life. Were there no devils, you would still have your hands full resisting the corruptions of your own heart. What Paul wants you to see is that your old nature is only a private in the war against your new nature. Satan comes to the battle as an ally of the flesh and launches a massive attack. He is the general who marshals your sinful inclinations, exercises them mercilessly, and sends them out as a united front against the power of God in your life. Compare it to the following situation. Suppose that while a king is fighting to subdue his own mutinous subjects, some superior foreign troops should join with them and take command. Then the king no longer fights primarily against his subjects, but against a foreign power. You see the spiritual analogy: Even as the Christian is fighting against his own inner corruptions, Satan joins his power to the residue of the old nature and assumes command. It could be said that our sin is the engine, and Satan, the engineer.
This knowledge should make every one of us diligent to keep our lusts unarmed.