“What the law could not do, in that it was weak through the flesh, God, sending His own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh.” –Romans 8:3.
In Romans 8:7 Paul writes: “The mind of the flesh is enmity against God; for it is not subject to the law of God, neither indeed can it be.” Here Paul opens up the depth of sin that there is in the flesh. In chapter 7 he had said that in the flesh there is no good thing. Here he goes deeper, and tells us that it is enmity against God: it hates God and His law. It was on this account that God condemned sin in the flesh on the cross; all the curse that there is upon sin is upon the flesh in which sin dwells. It is as the believer understands this that he will cease from any attempt at seeking to perfect in the flesh what is begun in the Spirit. The two are at deadly, irreconcilable enmity.
See how this lies at the very root of the true Christian life (vers.3,4): “God condemned sin in the flesh, that the righteousness of the law might be fulfilled in us who walk, not after the flesh, but after the Spirit.” All the requirements of God’s law will be fulfilled, not in those who strive to keep and fulfill that law — a thing that is utterly impossible — but in those who walk by the Spirit, and in His power live out the life that Christ won for us on the cross and imparted to us in the resurrection.
Would God that His children might learn the double lesson. In me, that is in my flesh, in the old nature which I have from Adam, there dwells literally no good thing that can satisfy the eye of a holy God! And that flesh can never by any process of discipline, or struggling, or prayer, be made better than it is! But the Son of God in the likeness of sinful flesh — in the form of a man — condemned sin on the cross. “There is, therefore, now no condemnation to them who are in Christ Jesus, who walk, not after the flesh, but after the Spirit.”