"The Monkey's Paw" is a rare story in that the theme is actually stated in the story. Sgt. Maj. Morris tells the Whites that the old fakir who put the spell on the paw said, "Fate rules people's lives and those who interfere with fate do so to their sorrow." The message is a warning, but Mr. White doesn't believe it. Even though Sgt. Maj. Morris makes it clear that he tried wishing with unfortunate results and he tries to throw the paw on the fire, Mr. White makes a wish for 200 pounds only to find that he receives the money when Herbert dies in a factory accident. According to the fakir, then, because Mr. White had wished for something he should not have had, his son lost his life.
The second wish that Mrs. White encourages him to make is for Herbert's return--one week after his death. When the strange knocking begins at the door during the windy night, Mr. White panicks, believing that the previously dead but still mangled Herbert could have walked home from the cemetary and is now at the door. Because he fears what his wife will find if she opens the door, Mr. White makes his third wish--for the noise to stop.
Therefore, he uses his three wishes and to his sorrow, loses his son and disappoints his wife, who fervently believed that their son was at the door. She wanted him back, regardless of his condition.