book theme

while i was reading my book i started to think what is the theme of this book, what is it trying to tell me. Why is it trying to tell me this. I think the theme of this book is to alwas fight through the pain and fight not for yourself but for the person fighting next to you. I think that this is the theme becuse the main character is a Navy SEAL and he says that if he where to fight for himself he would not have made it as far as he did but since he had his fellow brother in his mind who had died during battle right next to him that gave him the extra determanation to keep going. most of that determanation came from the fact that he promised his freind that he would give his wife a letter that he wrote right before he died. So marcus the main character was determaned to stay alive long enough to give his freinds wife that letter.