The ironic statement you make in your post is the beginning of a statement of the theme of this story. This is the story of a boy and his mother who are never satisfied with what they have and always want more. It is a very real and plausible situation for humans to have desires that just can't be satisfied but conversely feed the continual drive for more of whatever is desired. In this case, the family never thinks they have enough money. The real problem is that they live beyond their means, and even once the boy wins the money at the races and gifts it to his mother, it is quickly and rather frivolously spent. The bigger problem then is the need to maintain the most recent lifestyle expenses -- in this case, a very expensive education for the children. There is something very sad and pathetic about these characters and any people who cannot ever be satisfied. And it is that very reality that literally drives young Paul to death. He is absolutely consumed with the need to "see" the winner of the race, win the big money, and ease the imagined whispers for more money and therefore earn his mother's love and attention.
- It is ironic that the whispers of the house grow in intensity as the boy continues to make more money. It shows that chasing after more and more wealth doesn’t bring happiness, it only makes one want more and more. Christmas has become a time of wanting more and more. That is the point of the story - chasing after more and more wealth doesn't bring true happiness, it only makes you want more and more and more. And what better time than Christmas for the whispers to grow more audible? Christmas for many has now become nothing more than receiving and giving materialistic presents. The whispers seem especially audible at Christmas time as they are reminding them of their “materialistic” status and what they need to do in order to maintain it. The boy’s last speech is a message that no matter how much money you have, it doesn’t bring you any happiness. You may become lucky, but not happy.