The name Christians was first given at Antioch (Acts 11:26) to ‘the disciples’, to those who accepted the teaching of the apostles. There is no question of its being restricted to those who profited by that teaching as much as they should have. There is no question of its being extended to those who in some refined, spiritual, inward fashion were ‘far closer to the spirit of Christ’ than the less satisfactory of the disciples. The point is not a theological or moral one. It is only a question of using words so that we can all understand what is being said. When a man who accepts the Christian doctrine lives unworthily of it, it is much clearer to say he is a bad Christian than to say he is not a Christian.
C.S. Lewis, Mere Christianity (1952; Harper Collins 2001) xv