What is the theme in the book sold?

Some notable quotes from Patricia McCormick's Soldinclude:

“Simply to endure is to triumph.”

“If you look hard enough, chaos turns into order the way letters turn into Words.”

“This affliction--hope--is so cruel and stubborn, I believe it will kill me”

“Trying to remember, I have learned, is like trying to clutch a handful of fog. Trying to forget, like trying to hold back the monsoon.”