Answer:
I can be found after you remove 6 letters from BSAINXLEATNTEARS
found at the back of the book.
I am a box which holds keys but not locks. With the right combination, I may unlock your soul. What am I?
I am the key that is the hardest to turn
I am the only word that looks the same when spelled upside down.
Before I grow I'm small. When I'm old I grow tall. When I die I give a mighty fall.