Different ways of writing the same equation can suggest very different things, even if they are logically equivalent.... In Einstein's original 1905 paper, you do not find the equation E = mc2. What you find is m = E/c2.... the title of the paper is a question: "Does the Inertia of a Body Depend on Its Energy Content?" …If we can explain mass in terms of energy, we'll be improving our description of the world. We'll need fewer ingrediants in our world-recipe.

Ch. 3, p. 19. - The Lightness of Being – Mass, Ether and the Unification of Forces (2008)