But why is it C to the 2nd power? Why not to the 1st power or to the 3rd?

Update: Maybe this is the answer. Basically it is related to the formula for the area of a circle, Area=PiRadius[sq] where Area = Energy content, Pi = Mass, and Radius = speed of light.

I'll have to think about this, I guess. It is not intuitive since a circle is a two-dimensional structure. I think of energy and mass in terms of a three-dimensional world. In a three dimensional world, volume is based on the cube of the radius.