What would be a good thesis for the book A Farewell to Arms by Ernest Hemingway?

I can't think of a thesis for my book! You know like if I was reading the lovely bones i would say that the author is trying to say live life to the fullest. What is Ernest Hemingway trying to say in this book??? I HAVE NO IDEA! I was thinking maybe something like love will get you through the hard times. Idk...HELP!!?