“It is now technically impossible,” NT Wright says, “for the Christian to present his own or her own self to sin, since the self has died with Christ and been raised ‘ini order to live to God’.” But, Wright is quick to add, “What is possible — all too possible, alas — is for the Christian to present his or her members, the varied parts of of personality, mind, or body… to sin.” What Paul is speaking here is of logicalities not possibilities and of illogicalities not impossibilities.
The issue for Paul is what “rules and reigns” (kurieuo and basileuo). Baptism enables a person to die to sin, to law, and to self, and it also enables a person to live in resurrection, power, Spirit, and grace.
Paul is summoning his readers to let this grace work have its way in their lives; to live in grace, by grace, under grace and with grace.
What does “not under law” then mean? Law, you will remember, is a Jewish thing — given by God to his Covenant people in order to reveal sin. Once Law has done its thing, and the person has entered into the Messiah (“in Christ”), the Law’s work is over in the redemptive designs of God.
We are summoned to choose: either live in the Grace System or live in the Law/Sin System. Christ opens the way into the Grace System, and that is why for Paul it is illogical for those in Christ to find their way into sin and the law.