Answer:
The final lines of the poem rightly reassert the importance of community and how no man can be left alone to survive on his own, away from the other humans.
Explanation:
In his poem "No Man is an Island", metaphysical poet John Donne talks of the importance of a community/ social interaction for humans to be sane and civilized. No man living alone and away from other humans can survive on his own, irrespective of what may have been presumed.
And by ending the poem with the lines "and therefore never send to know for whom the bell tolls; it tolls for thee", he perfectly presents his point home by generalizing the death toll that is ringing for anyone. It could be for you or for me, but that's the uncertainty of life, for we know not when we will all die, but we will die one day, that is a certain fact. Being a part of a society or among people is needed for a man to thrive and survive. And one day, the bells will toll for thee. These final lines perfectly resonate the important theme of how man is a social being, and not to be left alone/ living alone.