How should believers serve?
Believers should serve in newness of spirit, not in the oldness of the letter. Having been delivered from the Law, they serve by believing the Gospel through faith plus nothing, not by legalism or fleshly effort. Service flows from the spiritual realm and the transformed life, rather than from Law-keeping.
Les explains that believers are delivered from the Law, which was an administration of death, so that they should now serve in newness of spirit and not in the oldness of the letter. This is the whole transformation of life in the realm of the spiritual. He asks how we get there, and answers: believe the Gospel. Les connects this to Galatians 3:3, where Paul asks if those who began in the Spirit by Paul's Gospel through faith plus nothing would now move into a deeper spiritual life by the flesh. The flesh wants legalism and Law, which is part of the old Adamic nature, but believers are not under that Law; they are in this whole new frame of thinking, the spiritual realm.