Whoever remains in him doesn't sin. Whoever sins hasn't seen him, neither knows him.

 What John is saying may be put down in four stages. (a) The ideal is that in the new age sin is gone for ever. (b) Christians must try to make that true and with the help of Christ struggle to avoid individual acts of sin. (c) In fact all men have these lapses and when they do, they must humbly confess them to God, who will always forgive the penitent heart. (d) In spite of that, no Christian can possibly be a deliberate and consistent sinner; no Christian can live a life in which sin is dominant in all his actions. 