Slaves no more. Sin's power over us WAS absolute. The thing we are told to do in 6.11 is an act of faith. See yourself the way God sees you, and the way He now wants you to see yourself. A dead body must be put away out of sight soon.
Burial puts the dead out of sight.
Since we have been buried with Christ, our old life is put away. There is a great contrast between the old selfish life and the new Christ-centered life. It is called the Old Man and the New Man which is created in knowledge, righteousness and holiness, the image of God. It is unthinkable that we should go on in the Old life we used to live, just as it would be unthinkable to keep a dead body around our homes. After Augustine was converted, a prostitute recognized him and tried to seduce him.