I've had a read around about some of the hidden themes and motifs that Jacobs uses to set the mood of the story. BE CAREFUL WHAT YOU WISH FOR! is the story's core message I suppose. Mr White only wishes for £200 - a small amount of greed considering all the riches they could of wished for - but the devastation it brings causes the destruction of the White family, and costs his wife and himself their sanity.
In all we have 5 characters. Each is necessary to tell the story correctly.
Mr White: The Husband. The Whites are portrayed as a comfortably living family. Mr White almost jokingly wishes for £200 thinking that no harm can come from wishing for such a small amount of money. In truth it is never truly revealed whether the Paw granted his wishes because all the events that happen in the story could easily be attributed to unlucky coincidence. Herbert might of died that day regardless and the unidentified knocker may just of been someone from the down the street asking for a pint of milk, but leaves after no one answers the door in reasonable time.
The evidence that the power of the Paw is real, lies in the identity of the person/thing knocking at the door but who/what it was, is never revealed... So the story is on one level about being greedy, but it's also about the guilt which the act of greediness will bring with it..
Mrs White: The Wife. Like the rest of the family at the beginning, she is a normal, gentle woman but the domino effect of the Monkey's Paw wish eventually drives her insane with grief over her lost son.
Herbert White: The Son. The only child the Whites have left. He unknowingly foreshadows his own death. He is killed the day after Mr White wishes for £200. Later the Whites wish for Herbert to be bought back to life. An unknown 'thing' bangs on their door late at night but it is never revealed whether said thing is indeed the re-animated and presumably mangled corpse of Herbert as Mr White wishes the door knocker away in the story's climax.
Sergeant Morris: An old friend of the Whites who has been in India for 20 years. He brings the Monkey Paw with him, and makes a half-hearted attempt to destroy it but willingly gives it to the White's knowing the destructive power it contains. A shady character for sure. I have a feeling his presence has something to do with a wish granted by the Paw...
Maw and Meggin's Representive: He informs the White's of Herbert grisly demise and hands them £200 compensation, the exact sum Mr White wished for.