What realm are believers in now instead of the oldness of the letter?
Believers are now in the newness of spirit, that is, the spiritual realm, rather than in the oldness of the letter, which refers to the Law. Having been delivered from the Law, they serve in this new frame of thinking by believing the Gospel, not by fleshly legalism.
Les explains that believers have been delivered from the Law, which was an administration of death, and are no longer held by it. Instead, they serve in newness of spirit, not in the oldness of the letter. The oldness of the letter is the Law. This is the whole transformation of life in the realm of the spiritual—a new frame of thinking. Les asks how we get there and answers: Believe the Gospel. He connects this to Galatians 3:3, where Paul asks whether 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, part of the old Adamic nature. Galatians 3:4 adds, Have you suffered so many things in vain, if it be yet in vain?