Truthfully, it is very hard to understand what lesson the fakir supposedly wanted to teach and why he thought it worthwhile to teach that lesson, whatever it was, to only three people. This part of the story only seems intended to explain why Mr. White gets to make three wishes. If everything that happens to everybody everywhere is predetermined because fate cannot be altered, then it was predetermined that Herbert would be killed at the factory and could not have been otherwise. A strong part of the complex Hindu religion is the necessity of giving up desire. As the Bhagavad-Gita expresses it in one simple verse:
He knows peace who has forgotten desire.
The sergeant-major may not have understood the intention of the fakir, who may have wanted to demonstrate that all desire is harmful. There are certainly many times in life when we regret having gotten something (or someone) we desired.
The fakir wanted to show people that fate ruled people’s lives.
When an old sergeant comes to visit the White family, he brings with him a mysterious trinket called the Monkey’s Paw. The sergeant explains its origins.
"It had a spell put on it by an old fakir," said the sergeant-major, "a very holy man. He wanted to show that fate ruled people's lives, and that those who interfered with it did so to their sorrow.
He goes on to explain that any man can make three wishes on the paw, and they will be granted, but this is a very dangerous thing to do. The Whites ask this old friend about the wishes. The answer is a powerful piece of foreshadowing of the paw’s meaning.
"The first man had his three wishes, yes," was the reply. "I don't know what the first two were, but the third was for death. That's how I got the paw."
The sergeant says he had his wishes granted, but refuses to say what they were. He only says that he keeps the paw out of “fancy,” and he does not know if he would have another three. Then he decides to burn it.
The Whites, however, are intrigued. They ask him how to use it, and he tells them. Mr. White wishes for money. He says he felt the paw move in his hand. No one believes him, and things go back to normal. The sergeant leaves, no doubt fully realizing that destruction is about to reign down on the household.
The Paw does grant your wishes, but wishing has terrible consequences. Mr. White gets his money, but he gets it when his son Herbert dies and Herbert’s employer compensates the family for the loss with two hundred pounds—the exact amount Mr. White wished for.
The Whites are devastated. The fakir has made his case. You can’t have something for nothing. If you want to mess with the fate, you have to pay the price. He has also proven that people are greedy. Given the choice of three wishes, they will inevitably take them. Even the sergeant, who has clearly seen the consequences of the Paw before, said he didn’t know if he would take the wishes again. That is why he tried to burn it.
I think the lesson in the story is to be careful what you wish for and to not be selfish. In the story, the couple makes a wish to come into some money, but they got it in a way that they didn't expect. This selfish wish caused harm to someone they loved and in turn made them regret what they did. When they tried to fix their mistake, it just made things worse. These events show what a self serving wish can do to people around you and yourself. You can't easily take back things that are said.