In this short story, we are told explicitly why the fakir put the spell on the monkey’s paw. Even if we were not told explicitly, we would be able to infer the reason from the moral of the story.
When the story begins, the White family is generally content. They seem to get along well with one another. They are not in the most luxurious circumstances, but things seem to be pretty good. But then Sergeant-Major Morris shows up with the monkey’s paw. The family gets greedy and wants to change their lives. This, of course, leads to tragedy. From this, we could infer that the fakir wanted to teach people to be content with what they have.
Sergeant-Major Morris tells us straight out what the fakir was trying to do. The fakir’s purpose was similar to the idea in the previous paragraph. Morris says that
He (the fakir) wanted to show that fate ruled people's lives, and that those who interfered with it did so to their sorrow.
The fakir wanted to show people that they should not try to change their fate. They should be content with the life that they have been given and should not try too hard to change their lives.