I hope you don't mind if I butt in here.
I don't know about other people, but I've found that the relationship that Einstein discovered between mass and energy is easy to forget. I tend to think of matter and its mass (measure of inertia) as distinct from energy which is defined as the ability to do work. If we equate mass and energy, we have the following:
the tendency of a body at rest to stay at rest and a body in motion to stay in motion = the ability to do work
Although the two characteristics may seem similar in some ways, they are hardly obviously the same.
Some physicists claim that matter and energy are much the same, though. At the subatomic level, matter appears to be essentially energy. At the macro level, the differences become much more pronounced. I believe that this paradox can be reconciled by noting the old maxim: the whole is greater than the sum of its parts. It's the way energy is "put together" to make matter that makes something like hydrogen or lead so much different than light or radio waves.
So what can we make of E = mc^2? Like much of science, it may be counterintuitive. But as anybody who has studied relativity or quantum mechanics can attest, the world we live in doesn't always make sense.