In "The Devil and Tom Walker", does Tom really change when comparing his behavior before he made the deal with Old Scratch, to his behavior when he grows old?
If you asked Tom, he would probably say that in his old age, he had learned from the mistakes of his youth, and was now a devout churchgoer and a friend of his neighbors, helping those in need through his business.
However, the omniscience of the narrator makes it clear that very little has actually changed about Tom's personal character; he's still miserly, thinks only of himself, and his attempts at penance are in fact self-congratulatory and fundamentally flawed. Tom was probably never capable of truly changing at all.
In his younger days, Tom is described as being unpleasant, miserly and generally concerned only with antagonizing his wife. The treasure that he negotiates his soul for, and the successful business that he creates with it, transform him into a person of high social standing, but it doesn't buy him class. He retains all of his worst personality traits, and gains some new ones, such as his ostentatious displays of wealth that are intended only to display that wealth for its own sake, something the narrator implies is a common practice for those with lots of money but poor character.
As Tom ages, he begins to fear death, and consoles himself by going to church and reading a Bible frequently, but he does these things as if penance was a competition, and he will "win" by being the loudest and most noticeable, carrying his ostentation over into his religion. It is suggested that Tom thinks he is somehow protected by doing these things, despite the fact that he continues to commit the same sins through his business that his arrangement demanded in the first place.