Apparently Einstein could not finish the formula completely because the other two forces were not incorporated. The Strong and the Weak Forces need to be today incorporated with the Gravity and Electro-Magnetic forces.
The equation was complete from the very beginning
It simply, so to speak, claims that the content of energy contributes to the mass of the body
The higher the temperature the heavier the body
Even though the weight difference is not measurable because of the huge coefficient c^2
A common misconception is that the equation, by itself, entails the existance of nuclear energy or even of "Matter annihilation"
That's false
