In Romans 6:12 Paul begins to address the issue of Christian ethics. The new perspective of the life lived for the glory God with the risen Lord does of course affect the earthly existence of believers. The redeemed should refrain from once again entering into the service of sin; we have a new Lord now, and serving him is what a life of grace apart from the law means.
In this passage Paul continues to personify sin. He contrasts it to a life lived in the presence of God through the risen Lord: Let not sin therefore reign in your mortal body, to make you obey its passions.
In the Greek text of most manuscripts the direct connection between sin and our passions is even clearer: Do not obey her (autèi) through your passions.
Paul’s view is that sin stirs up the passions and desires, while these same passions and desires are conquered by the Spirit. Unbridled desires lead one to submit to the reign of sin. Our mortal body (our old self,
Romans 6:6) is now governed by sin. Yet the time of subjection to its rule is now over. Therefore, we ought not obey it (again) through our passions!1
12 Let not sin therefore reign in your mortal body, to make you obey its passions.