Mere Christianity, in The Complete C. S. Lewis Signature Classics

pp. 38-39

“Fallen man is not simply an imperfect creature who needs improvement.: he is a rebel who needs to lay down his arms.  Laying down your arms, surrendering, saying you are sorry, realizing that you have been on the wrong track and getting ready to start life over again from the right one—that is the only way out of our ‘hole.’  This process of surrender is what Christians call ‘repentance.’  Now repentance is no fun at all.  It is something much harder than merely eating humble pie.  It means unlearning all the self-conceit and self-will that we have been training ourselves in for thousands of years.  It means killing a part of yourself, undergoing a kind of death.  In fact it needs a good person to repent.  And here comes the catch.  Only a bad person needs to repent: only a good person can repent perfectly.”  Lewis goes on to present the work of Christ: “He could surrender his will, and suffer and dies, because he was man; and he could do it perfectly because he was God.”  Lewis then adds that we surrender, repent, only by sharing in Christ’s death and resurrection, just as we are intelligent or wise only by sharing in God’s intelligence and wisdom.

p. 40

We repent only by sharing in Christ’s death and resurrection.  We somehow die and rise with him (a central Pauline teaching, as in Col. 2 and 3, Rom. 6, and Gal. 2:19-20), thereby starting a whole new life.  Does it sound odd?  It is—just as how we acquired, “without our consent,” our ordinary, mortal lives.  It was “a curious process” involving our parents—a process children spend years trying to guess and then can hardly believe.  It is the same with our new life: we acquire it by a process we can hardly believe.