"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 put a spell on it so that three separate men could each have three wishes from it." (1.26)
This implies that the paw is just plain evil, that any wish made on it will have bad consequences. It sounds like a caution against using magic to change the course of our lives. Since most of us don't have access to magic, it could be read as warning against trying to get things the easy way, or against taking unnecessary risks – such as gambling.
"If you could have another three wishes," said the old man, eyeing him keenly, "would you have them?" […]
"I don't know," said the other. "I don't know." (1.38)
The paw seems to bring out greed and desire in those who come in contact with it. To some degree, it seems to have the power to rob people of their free will.
"I suppose all old soldiers are the same," said Mrs White. "The idea of our listening to such nonsense! How could wishes be granted in these days? And if they could, how could two hundred pounds hurt you, father?" (2.2)
Here's what Mrs. White is basically saying: since the paw can't really grant wishes, there can't be any harm in wishing on it. Later it seems she really does believe in the paw and is trying to convince her husband to use it. This helps us see that beneath her cheerful demeanor, she is a little desperate for anything that might turn their lives around.
"The firm wished me to convey their sincere sympathy with you in your great loss," he said, without looking round. "I beg that you will understand I am only their servant and merely obeying orders." (2.25)
The man from Maw and Meggins (probably the company that owns the factory where Herbert worked) explains that he doesn't necessarily agree with what he's about to do. He doesn't want the Whites to think he is as unfeeling as the firm he works for. Like the Whites, he seems to feel his life is out of his own control. He is caught between his own will and the will of his employers. Is he as powerless as he claims?
"No," she cried, triumphantly; "we'll have one more. Go down and get it quickly, and wish our boy alive again." (3.17)
Mrs. White is used to being able to control her husband. Here she is able to convince him to wish Herbert alive, even though he really doesn't want to. What gives her this power over him?
"We had the first wish granted," said the old woman, feverishly; "why not the second."
"A coincidence," stammered the old man. (3.22)
Here Mr. White is making an argument that Herbert's death happened because of the dangerous conditions where he worked. He doesn't want to believe he caused Herbert's death by wishing on the paw. The fact that he stammers these words suggests that he isn't entirely convinced of this.
He heard the creaking of the bolt as it came slowly back, and at the same moment he found the monkey's paw, and frantically breathed his third and last wish. (3.48)
We don't know what Mr. White wishes here. The important thing is that he makes the wish on his own, free of his wife's or son's influence, based on what he thinks is right.