Why do believers still struggle with the old nature if it is dead?

Believers still struggle because God reckons the old Adam crucified and dead positionally, yet in experience that old nature remains present, pursuing and plaguing them. The new nature from salvation and union with Christ wages constant warfare against the old sin nature until they leave this mortal body.

Les teaches that believers do have two natures: the old Adam, who constantly pursues us, and the new nature that comes from the salvation experience and union with Christ. This is Pauline doctrine, describing a constant warfare between the old sin nature and the new divine nature. In Dying Daily, the believer must keep old Adam in subjection and put him to death. Romans chapter 6, especially verse 13, deals with reckoning old Adam as our mortal enemy and constantly putting him to death. Though it may sound like double talk, God in His omnipotence and sovereignty reckoned our old Adam as crucified with Christ the moment we believe. He is dead, but in experience he is still with us and will plague us until we leave this body of mortality.

How long will the believer struggle with the old nature?

The struggle with the old Adam continues throughout this earthly life. Although God reckoned the old nature crucified with Christ at salvation, in experience it remains and plagues the believer. Only when leaving this body of mortality does the conflict with the old sin nature finally end.