What is not eternal is eternally outdated.
I just finished this amazing trilogy and it inspired me to recommend it. It is indeed a great deal of theology put in a thrilling story. You can read a lot about C.S.Lewis' opinion on different topics and it is filled with eternal principles - some of them questionable, some new nevertheless applicable, some even trivial.
What about our lives is eternal, what is not. Everything that is not eternal, will be gone forever or "outdated forever". There is an answer to that problem in the first book of the trilogy: one of the Hrossa tells Ransom (the protagonist) that no event is amazing standing alone - rather the joy of looking forward to it, the event itself and the awe of remembrance altogether make the event amazing to us...
but read for yourself.