No one can become a disciple of Jesus Christ without beginning a lifelong battle with sin, and he can never give up this battle. He is promised victory but he must still personally fight the good fight of the faith to the end.
John’s statement of what is evident to all is designed to confront those who try to deny what is obvious in their attempt to side-step the plain statements of Scripture. Our consciences need to be reminded constantly that sin is sin, because the flesh has a thousand ways of trying to get round the commandment.