How does Emily's experience in Act III relate to the overarching theme of "Our Town"?
In Act III, Emily has become one of the "passed on". She is greeted in the graveyard by her deceased family and friends. She is not ready to be there, however. She still talks of the daily goings-on in Grover's Corner. She insists on returning there, choosing the happiest moment of her life to return to. It is Emily's belief that she will be happier reliving her 12th birthday than she is in trying to accept her death.
However, Emily is stung by bitter feelings when she returns. She realizes how unknowing she was back then, how unknowing all the living people are. She understands that she always took life for granted. The pain is too much, and she returns to accept her death.
This realization portrays Wilder's meaning. He is emphasizing the beauty of life and the human experience. This is why he chooses a small town that represents the simple beauty of America and includes characters from all walks of life. He is showing audiences that each day, despite its struggles, is a gift and we must all enjoy it.