what is the meaning and purpose of a long way from chicago?

Coming of age is a major theme in the story. Every kid dreams about a day when he or she becomes an adult. Joey and Mary Alice are not an exception. At first they are reluctant to come to their Grandma’s place, but even they understand that it is temporary. Time flies too fast and their wish to become adults comes true, but it doesn’t make them happier. For instance, Joey is going to see the horrors of the World War II with his own eyes. The train that he takes to get to a military base goes through his Grandma’s town. He waves at it, his Grandma and his childhood. This is a bittersweet farewell.