Because of the antichrist teachings that arose among them, John is reminding the flock of the truth of the Gospel message in contrast to the teachings of these antichrists. Those who have confessed and repented of their sins, are cleansed from all their sins, and having been cleansed from all unrighteousness, they have no sin whatsoever. They have been washed as white as snow and have been freed from their sin. There is no sin in Christ. O man, how then do you manage to be sinning in Christ?