In Part III when Mrs. White insists on her husband's wishing for Herbert to come back to them, he tries his best to talk her out of it. But she is adamant. She cannot make the wish herself because only the owner of the monkey's pay can use it for that purpose, and it was established early in the story that Mr. White was the owner because he had insisted on paying Sergeant-Major Morris a small amount of money for it. The sentence in the story that best indicates White's true feelings about bringing Herbert back to life is the following.
"He has been dead ten days, and besides he - I would not tell you else, but - I could only recognize him by his clothing."
White had to go down to the textile mill and identify his son's body. He never told his wife what Herbert looked like after being torn up by the machinery. This warning to his wife is mainly intended to inform the reader that if Herbert comes back to life he will look truly horrible. He was not only mangled beyond recognition, but he has been rotting in a grave for ten days. The reader never gets to see Herbert--if it truly was Herbert who was pounding at the front door--but the reader can imagine what Herbert must look like. He would not only look like a monster but he might behave like a monster, after being dead for ten days and now returning to become part of the family again. He certainly couldn't be the same cheerful, happy-go-lucky young man he had been before the accident. It is no wonder that Mr. White has a change of heart and makes the third wish which causes the knocking to cease.
White must not have believed that the monkey's paw could really grant wishes when he made the second wish. He made that wish to pacify his wife, but he must have been hoping it would be ineffectual. After all, his first wish for two hundred pounds was simple and could have been fulfilled by sheer coincidence; but this second wish would be fantastic, it would be like trying to change the laws that governed the universe.
Then in the middle of the night the candle in their bedroom burns out. Mr. White gets up and goes downstairs to get another candle.
At the foot of the stairs the match went out, and he paused to strike another; and at the same moment a knock came so quiet and stealthy as to be scarcely audible, sounded on the front door.