The book opens with the following:

No man is an Iland, intire of it selfe; every man is a peece of the Continent, a part of the maine; if Clod bee washed away by the Sea, Europe is the lesse, as well as if a Promontorie were, as well as if  a Mannor of thy friends or of thine owne were; any mans death diminishes me, because I am involved in Mankinde; And therefore never send to know for whom the bell tolls; It tolls for thee. - John Donne

Pretty powerful, huh.  I think so anyway and it definitely sets the tone for this classic novel by the great Ernest Hemingway.  Many would say this is a must read just because it is written by one of the greatest writers of all time; I would say forget that and read it because it is a great story.

The whole story takes place over a few days in th mountains of Spain during their civil war.  The main character, Robert Jordan an American mercenary, falls madly in love with Maria.  So, at its core it is a love story but it is also about the pains of war and of faith.  It is beautifully written and you'll feel every emotion that Robert Jordan feels.  You'll believe that you're in the war, that you're eating Pilar's food in cave. 

Read it if you haven't, read it again if you already have.