What does the mahogany coffin symbolize in 'The Scarlet Ibis'?

The coffin symbolizes the possibility that Doodle is going to die at some point in the story. The coffin had been made because Doodle's death was imminent, but he lived. Never the less, the coffin was kept, presumably because it might be needed after all. Had the coffin been thrown away, that would have been a symbol that Doodle would probably live.