Why don't the desires of the old nature show up when you walk in the Spirit?
Walking in the Spirit means living under the Holy Spirit’s power and control. Because the Spirit never leads a believer into sin, the old Adamic nature’s lusts—though still lurking—do not come to the fore or get fulfilled. The Spirit’s control prevents those desires from surfacing and governing behavior.
Les explains that “walk in the Spirit” refers to the Holy Spirit, meaning to walk in His power and control. In that state, the believer will not fulfill the lusts of the flesh. Les illustrates that the Holy Spirit will never tell a believer to steal, commit adultery, or gossip. Although the old Adamic nature and its desires are still lurking in the background, when the Holy Spirit is in control, those things do not come to the fore. Paul calls this old nature the flesh, the old Adamic nature, which lusteth or desireth—what Les renders as “wareth.”