"In the eyes of many physicists Einstein’s move emptied the universe not only of the ether but also of its intelligibility and unity which, in the form of a hallowed scientific dogma, had been equated for the previous 300 years with mechanical interaction. Actually, Einstein’s move made the genuine content of the term universe more unified than ever, and also far more intelligible and meaningful. Indeed, the first step in saving the beauty of Maxwell’s equations was the unification of the speed of light by the postulate that its value remains in a vacuum always the same, regardless of the velocity of the emitting source, a postulate inconceivable within classical mechanics. An equally startling though logical consequence of Einstein’s procedure was the unification of matter and energy. Their equivalence became a common place through the formula E = mc2 . Another, and no less important consequence was Einstein’s almost immediate interest in extending his work from frames of reference that moved with respect to one another at any given velocity, to frames of reference accelerated with respect to one another. Such an acceleration was exemplified by the gravitational field produced by any mass. Unlike Special Relativity, General Relativity had therefore to have momentous cosmological consequences. They were spelled out by Einstein himself in 1917 in a paper in which for the first time cosmology came into its own, that is, achieved the status of a scientifically consistent discourse.”
~S.L. Jaki: Cosmos and Creator, Chap 2—The Cosmos of Science.