What does Romans 6:12 mean?

In the previous verse, Paul told us to think of ourselves as dead to sin and alive to God in the same way that Christ is dead to sin and alive to God. Now he tells us not to let sin reign or rule in our current, mortal bodies. We must not let sin make us obey it.

This strikes some readers as confusing. Hasn't Paul said that we are dead to sin (Romans 6:1)? Hasn't he told us that the "body of sin" has been done away with (Romans 6:6) and that we have been set free from sin by dying with Christ when we trusted in Him (Romans 6:7)? So how could sin possibly rule in us or make us obey its passions? The simple answer is this: We have been freed from the authority of sin over us, but we have not lost the desire to sin. In short, sin still appeals to us. It's easy for us to forget, or even to disbelieve, that we never again have to do any sinful thing (1 Corinthians 10:13). We are not slaves to sin. We can only volunteer.

Paul commands us to have that conversation with ourselves on an ongoing basis. He commands us to engage in that battle with our desires. Don't let sin tell you what to do, he writes. For the saved Christian believer, sinful desires are not the boss anymore. Christians should not give over control to those urges.