It's a unit of transfer. A unit holding and then transfering value, across transactions. That's a good service, which billions shall find useful. That service is all Bitcoin does, so it's a pure play device. Many other units of transfer are not pure plays, so over an extreme long term timeframe they can suffer from problems that won't affect Bitcoin.

Bitcoin may give the world a clearer yardstick reference point for units of value. Bitcoin can change the world by giving the world a better unit to measure value, to hold value and to transfer value.