Well, in my opinion, there is only one major theme in A Farewell to Arms, by Ernest Hemingway, and then some less important ones. Well, now's as good a time as any to get to it. :)

The major theme of the entire novel is, in my opinion, that death is the end of all things. In the beginning of the book, Catherine talks about how death is the end of all things. "...then of course he was killed and that was the end of it." (P.19) In the beginning of the novel, Henry just can't accept this. He is looking for something to believe in, a belief system of some sorts, one other than the standard Christian system. This is what really he looks for throughout the novel, even while he is involved with Catherine and when he is fighting in the war (well, not really fighting, more like driving an ambulance, but you know what I'm talking about.). It isn't until the very end, when he loses Catherine, the he figures out that death really is the end of everything, and he has finally found what he has been looking for all along.

Another theme of the book, but not as important as the first one, is love. I know thats a kind of broad and vague theme, but it exists in the book nonetheless. When Henry first meets Catherine, he is physically attracted to her, but doesn't want to fall in love. He's only interested in physical pleasures (not to say thats a bad thing, mind you). But as the novel progresses, he realizes that being with her is better than being with any prostitute (aww, how sweet), and that without her just doesn't feel "right".

Also falling into the "love" category, in another way, is his reason for deserting the Italian army. He hates the war, and sees it as pointless. So, in a way, he doesn't "love" the war, so he feels neither remorse nor (or should it be "or"? That always confused me some) regret for leaving. It is also this lack of love, except this time more widespread, that causes everyone else to tire of the war. I mean, c'mon, how much war can you take? They're tired, and want the war to be over.

For some reason, this whole last paragraph seems a little "off", I hope you know what I'm talking about. Its getting late, and I don't think I've had enough caffeine today to maintain any level of coherency much longer. Thankfully, I just have the Response section left, so I can afford to not make sense. :)