Why is the setting of the underworld important to the development of the theme

contributes to the plot and the characters of a story so much that without a setting, there will be no plot for the story to be held.

The configuration of the underworld is important to locate the reader, where the theme is being developed, how the characters relate to that place, what can happen in a place like this, among other things. In short, the configuration of the underworld is important because that is where all the action developed for the theme will occur.