Lewis concludes Book 4 with a polemic on the difference between "being nice" and being redeemed, as well as the necessity of losing oneself in order to find real Life in Christ: Give up your self, and you will find your real self. Lose your life and you will save it. Submit to death, death of your ambitions and favourite wishes every day and death of your whole body in the end: submit with every fibre of your being, and you will find eternal life. Keep back nothing. Nothing that you have not given away will ever be really yours. Nothing in you that has not died will ever be raised from the dead. Look for yourself, and you will find in the long run only hatred, loneliness, despair, rage, ruin, and decay. But look for Christ and you will find Him, and with Him everything else thrown in.

https://www.youtube.com/watch?v=tPfsHEgs_9E