a. Money(currency) has limited supply in circulation to avoid inflation.

b. To be sincere, the purpose of money is just to be spent, even if you save, you'll still spend at the right time. And guess what? It goes to the hand of another.

c. Multiple streams of income, ideas for creation of wealth. I'm gonna add to what @miraclehands said(he virtually took the words out of my mouth). Hard work pays, smart work pays faster, combination of both.... Unending flow of income