The drama is in the exponent.

Mass-energy equivalence is the principle that mass and energy are two forms of the same physical quantity, captured by Einstein’s famous equation E = mc². Because the speed of light squared is an enormous conversion factor, even a tiny amount of mass corresponds to a vast amount of energy. The equation does not mean matter casually disappears into energy; rather, it describes how the total mass of a system reflects its stored energy. It reshaped our understanding of matter, radiation, and the structure of the universe. It is used primarily in nuclear physics, particle physics, and astrophysics.