In a nutshell it explains why punishment and reward are not a good motivators for people with jobs that require cognitive skills. It all boils down to the human quest for mastery (of a skill or subject), self direction, and purpose. In other words we do things because we like feeling good about what we’re doing.
Money (reward) only enters the motivation equation when it reaches a level that frees people from financial stress, giving them the opportunity to feel masterful, self directed, and purposeful.
It also explains why open source communities are so successful and why companies that provide ‘free time’ for innovation are so successful.