Why can believers be comforted in their struggle against Satan?
Believers are comforted because the One within them—the Holy Spirit—is greater than the powers of Satan. Although Satan works through the old Adamic nature, the indwelling Spirit strengthens the new nature, enabling believers to suppress the old nature and find comfort in God's greater power.
Les teaches that Romans 7 describes the conflict between the new nature prompted by the Holy Spirit and the old Adamic nature. The old nature still slips in and causes failures, so believers must constantly keep it in suppression. While Satan works through that old nature as his playground, the believer has the Holy Spirit within, and He is greater than the powers of Satan, providing comfort in the struggle.