All of us were born in sin and were therefore "by nature" the children of the devil. That's the reason we sinned. Our sins don't corrupt our nature, but our corrupt nature makes us sin. That's why we must be "born again" and become new creatures (or a new creation) in Christ.

The Bible teaches that everyone was born with a sin nature or old man. For the Christian, the old man is dead. We do not have a nature that is driving us to sin. If that is the case, then why do we seem so bound to sin even after we experience the new birth? The reason is that our old man left behind what Romans 6:6 calls a body. 

Just as a person's spirit and soul leave behind a physical body at death, so our old man left behind habits and strongholds in our thoughts and emotions. The reason a Christian tends to sin is because of an unrenewed mind, not because of a sin nature.

Our old man ruled our thinking before we were born again. He taught us such things as selfishness, hatred, and fear and he placed within us the desire for sin. The old man is now gone, but these negative parts of his body remain. Until renewed, our minds continue to lead us on the course of our old man.

To experience the resurrection life of Jesus, we have to know that our old man is dead. Then, through the renewing of our minds, we destroy the body that the old man left behind. The end result is that we will not serve sin any longer.