The Difference Between Being a Christian and Being 'In Christ'

I'm currently reading 'I Believe in the Holy Spirit' by Michael Green, and he makes an interesting (though only passing) point that in the New Testament the term 'Christian' is only found on the lips of pagans. The New Testament's favourite term - at least, Paul's favourite term - to describe followers of Jesus is to speak of us as being 'In Christ'.

What's the difference between understanding yourself as a 'Christian' and understanding yourself as being 'In Christ'. The former is a label which identifies an allegiance to a particular school of thought. It means as much as 'pacifist', 'conservative' or 'racist'. The latter instead refers to an actual state of being; an identity. Being a follower of Christ is not simply a matter of subscribing to a specific philosophy, but rather it's a matter of becoming a new creation. It's a matter of having a totally changed identity. It's a matter of a genuine and real transformation. If I am just a Christian then I can remove that label when I no longer believe what I used to believe, but if the real me has been changed in some way - if I am now 'In Christ' - then this leaves scars that can't simply be dropped and forgotten when I wake up in a bad mood.

Do not see yourself as being a 'Christian' - that's how the Pagans see you. Instead, see yourself as being 'In Christ'. It makes all the difference in the world.