There are three ways Christians deal with sin in their life.  One is not to acknowledge it at all, in that they don't believe the law applies any longer.  Without the law, there is no sin, no need for sanctification.  the other extreme is to believe that God justified and sactified the believer.  Therefore, they are incapable of sin.  Against both of these views, Paul explains that the battle over the sin of the old man is still within every believer.  However, the believer is not to be dominated by sin.  This is reality. Every Christian's battle.