To be transformed is to be irrevocably changed. Once a caterpillar becomes a butterfly, it can no longer be a caterpillar again. Butterflies never return to being caterpillars, nor do those saved by the cross of Jesus go back to a life ruled by sin.

The end of Romans 5 says that where sin increases, so does grace. To the sinful mind, this sounds like an invitation to sin more to get more grace. In Romans 6, Paul responds by teaching what it means to be transformed. Yes, more sin equals more grace, but the response by one transformed by the gospel is not to desire more sin but more righteousness.