Of Mice and Men question? Exam tomorrow, save me please!?

Hello:) The question which i am in dire need of an answer to is What is the message or what is Steinbeck (the author) trying to tell the reader? Like, what is the message or 'moral' of the book. This is something that i really want to go into a lot of depth into in my essay, and as a straight A* student in English i am drawing a blank on this one! Any help related is greatly appreciated, thanks in advance! P.S Any other clever info to point out about the book in my essay is extremely helpful!