What is the theme of the story "The Rocking Horse Winner," written by D.H. Lawrence?

Greed is a major theme of this story.  Paul is a selfless boy wanting to help his family.  His mother is a greedy and selfish woman, wanting not to make the family comfortable, but to buy pretty things.  Her greed causes her to lie and sneak, hiding what should be shared from her husband and the rest of the family.  Lawrence not only demonstrates the negative effects of her greed - Paul's death and the conflict within the family - but he also demonstrates the effect of greed on itself.  Greed increases unto itself.  For a greedy person, the more they get, the more the want.  The are never satisfied, as is clearly true of the mother in this story.  She could have $1000 a year to make her comfortable, but she demands all the money at once - which of course leads her to spend it all at once.  Ultimately, her greed destroys Paul and, ironically, the chance the family had to become undeniably wealthy.