How does the satire in "The Devil and Tom Walker" apply to all humanity?
If you read this short story with an eye to the satirical and ironic statements, you can answer this question. These statements get at the heart of the story and the theme. For example, right in the beginning, we find a reference to the fact that the story took place during a time when there were many earthquakes that "shook sinners" to their knees. This is a satirical comment that the only time people are prone to pray is during times of great crises in their lives. Later on, we find out that Tom Walker and his wife have a dysfunctional relationship, are always fighting and yelling at each other and trying to cheat each other. When people come upon them, the people quickly run the other way, "rejoicing, if a bachelor, in his celibacy." This is a satirical comment on marriage - better to be single than married to a shrew.
As Tom Walker is heading home one night, he decides to take a shortcut and Irving says that "like most shortcuts, it was "an ill-chosen route." This comment warns humanity that shortcuts are not always the best route in life. If Tom had gone home the long way, he would not have encountered the devil.
If you continue in this fashion, you will find much more satire that applies to humanity in general.