Washington Irving, in "The Devil and Tom Walker," warns readers about sin and temptation. Tom Walker and his wife are both greedy. Money rules the life of each (to the point where each fears the other may try to steal from him (Tom) or her (his wife)). Given the chance to possess a fortune, Tom must give up his soul and become a usurer (a person who lends money at an outrageous rate of interest). Since Tom is so greedy, he takes the Devil's deal.
Prior to taking the Devil's deal, Tom's wife tries to bargain with the Devil. He refuses her, and she does not return home. Tom believes that the Devil has taken her. Now, with no one to share his fortune with, Tom sells his soul to the Devil. In the end, Tom pays for his sin (greed and giving into temptation) with his life.
Therefore, Irving's message behind the text relies upon the reader's understanding that sin and temptation are costly (Tom paid with his life). Although secondary, Irving is also suggesting that people should be happy with what they have and not try to get more through questionable or sinful means.