What is the main idea in the story a game of catch by Richard Wilbur?

The main idea in "A Game of Catch" by Richard Wilbur is the theme of mortality and the passing of time. The poem uses the imagery of a game of catch between a father and son to explore the inevitable progression from youth to old age. It highlights the bittersweet realization that time is fleeting and that eventually the roles of parent and child will reverse.