How does a believer get control over the failures of the body and the old nature?
To control the failures of the body and old nature, the new nature prompted by the Holy Spirit must be strengthened and become uppermost in all thoughts, acts, and deeds. The believer must constantly keep the old Adamic nature in suppression, relying on the indwelling Spirit who is greater than Satan's powers.
Les explains from Romans 7 that the struggle—doing what one does not allow, hating what one does—shows the new nature, prompted by the Holy Spirit, recognizing wrong while old Adam still slips in. To control the failures of the body, this new part must be strengthened and become uppermost in all thoughts, acts, and deeds, constantly suppressing the old Adamic nature. While 'the devil made me do it' is rarely the case—it's old Adam—Satan works through that old nature as his playground. But the believer has Him within, greater than Satan's powers, providing comfort.