Here is the difference. Lewis assumes that God is good no matter what the results, Kushner assumes that God must do things our way in order to be good. It is a totally different approach to the view of man, God and the purpose of life. Lewis has a view that is Biblical. Kushner has a view that fits in very well with the post-modern philosophy of today.
The eternal God of the Bible is not safe. He is holy. That has consequences. We cannot play like we are Lucy (as in I Love Lucy) and He is Ricky. Yes, He forgives. Yes, He sent His Son to die for our sins. Yes, He is compassionate and merciful. He is also holy and He doesn’t play games.
(Hebrews 9:22 NAS77) And according to the Law, one may almost say, all things are cleansed with blood, and without shedding of blood there is no forgiveness.God did not cut himself any slack. Without the cleansing of the blood He won’t cut us any either.
homo unius libri