"Jesus answered them, Verily, verily, I say unto you, Whosoever committeth sin is the servant of sin." -John 8:34, KJV.

We are all born sinners, and, therefore, we are all born servants of sin. As we accept Christ, this mandatory service is removed, but our sin nature is not. When we sin against God, we willingly place ourselves under the service of sin again. We do this completely voluntarily, and this is such a slap in the face against God. He paid the ultimate price to remove our sins, and we go right back to serving them. We need to remain servants of Christ, not servants of sin.