Why does every believer still struggle with sin if the old nature has been crucified?
God has reckoned the old Adamic nature crucified and dead in Christ, but in experience it remains present with the believer. It is defeated and placed under the new nature's subjection, yet its influence still must be wrestled against. That is why believers still struggle with sin.
Les teaches that the old nature has been reckoned as crucified: God saw the believer in Christ on the cross, in the grave, and in resurrection, so the believer is resurrected in newness of life. Yet Paul explains this from the believer's point of view: he still has to wrestle against the influence of the old Adamic nature even though God has reckoned it crucified. God declared it dead, but in experience it is still with us—though defeated and placed under subjection to the new nature that came in by the power of God. This explains the confusion of verse 15: what I would, I do not; and what I hate, I do. Les says this is not really confusing because Paul is talking about these two natures, and he points to Galatians 5:16-17 to clarify.