The main theme is the danger of interfering with fate. The monkey's paw has the power to grant wishes, but every wish comes with unforeseen and often terrible consequences. It shows that people should be careful what they wish for as it might not turn out as expected.
Well, the theme of 'monkey paw short story' is about the perils of getting what you think you want too easily. The paw seems like a magical solution to people's desires, but it brings only misery. It's like a cautionary tale that warns against the greed for instant gratification. When the characters make wishes, they don't consider the potential negative outcomes that could come with having their wishes fulfilled.