From Alan Jacob's The Narnian:
Transformation is not optional but mandatory for Christians. This was Lewis' consistent position. After all, he had undergone his own transformation, discovering "depth under depth of self-love and self-admiration" and submitting to the life-long discipline of being purged of such sin. We must die in order to live,�hate our lives in order to find them, give up what we think of as ourselves in order to�gain our true selves. And this is the most difficult of tasks.