In Romans 12, Paul shifts his focus from instruction to exhortation; from “indicative” [the settled facts] to “imperative” [commands]. Chapter 12 – 15 is the application of the truths of chapter 1-11 [with a particularly close relationship to chapter 6].
Paul has made clear in Chapter 6: deliverance from the penalty of sin is inseparable from the deliverance from its power. We often repeat in Sunday school that:
The same gospel that satisfies the penalty of sin also breaks sins power over us.
The same power that saves you also sustains you [sanctifies you] .
Your union with Christ in his death and resurrection provides both! This leads to the truth that Jesus Christ is Lord; and to believe in him means at the same time a commitment to obey him. [Rom 1:5, 16:26 and 15:18] The “imperative” [command] of a transformed life [12:2] is therefore not an optional 2nd step after we are saved; it is part of the gospel itself!
Remarkably this truth is grounded in the fact that even when we obey, it is not something we do on our own, but through the grace, mercy and provision of God! Our obedience is not just because of the grace God has given to us in the past [Rom. 1-11], His grace is the continuing source!