This is a good question. Fate is all over the place, even if it is not mentioned all that much. Let me give you the context and give you some points.
The story concern three main people: the Whites, their son Herbert, and sergeant-major Morris, who gives the family the monkey's paw. Sergeant-major Morris tells the family that the monkey's paw has powers to grant three wishes. At first the family is skeptical, but when they do make a wish it comes true. However, it is at a huge price.
The family asks for money to pay off their mortgage and suddenly the money comes, but it is though the death of their son Herbert, who is killed in a machine accident at work. When this happens the family in desperation ask for Herbert's life back and they hear a knock on their door, which frightens them. They believe it is their dead son. Finally, they ask for their son to remain dead and the knocking stops.
The point of the story is that when you try to manipulate fate, there will be a price to be paid. No one can beat fate.