And now we begin to see what it is that the New Testament is always talking about. It talks about Christians ‘being born again’; it talks about them ‘putting on Christ’; about Christ ‘being formed in us’; about our coming to ‘have the mind of Christ’.
Put right out of your head the idea that these are only fancy ways of saying that Christians are to read what Christ said and try to carry it out—as a man may read what Plato or Marx said and try to carry it out. They mean something much more than that. They mean that a real Person, Christ, here and now, in that very room where you are saying your prayers, is doing things to you. It is not a question of a good man who died two thousand years ago. It is a living Man, still as much a man as you, and still as much God as He was when He created the world, really coming and interfering with your very self; killing the old natural self in you and replacing it with the kind of self He has. At first, only for moments. Then for longer periods.
Finally, if all goes well, turning you permanently into a different sort of thing; into a new little Christ, a being which, in its own small way, has the same kind of life as God; which shares in His power, joy, knowledge and eternity.
From Mere Christianity by C S Lewis