The main theme of the book is about war and 'Billy Pigrims' experience of this. I think it goes much deeper than this looking at an alternative meaning to 'life and death'. Whether we do actually die or live our same life over several times. Or whether Billy was truly insane or in fact experiencing all his time traveling. But then again I do tend to read more into things.. sometimes!
Slaughterhouse-Five. Kurt Vonnegut, 1969. The story is told in a nonlinear order and events become clear through flashbacks (or time travel experiences) from the unreliable narrator who describes the stories of Billy Pilgrim, who believes himself to have been in an alien zoo and to have experienced time travel.