http://www.phrases.org.uk/meanings/for-whom-the-bell-tolls.html
"Perchance he for whom this bell tolls may be so ill, as that he knows not it tolls for him; and perchance I may think myself so much better than I am, as that they who are about me, and see my state, may have caused it to toll for me, and I know not that.
...
No man is an island, entire of itself; every man is a piece of the continent, a part of the main. If a clod be washed away by the sea, Europe is the less, as well as if a promontory were, as well as if a manor of thy friend's or of thine own were: any man's death diminishes me, because I am involved in mankind, and therefore never send to know for whom the bells tolls; it tolls for thee."