Sure, one simple sentence is not going to explain the universe. But, at least from the simple relativity side of things, essentially everything falls out of (that is, it's a consequence of) that simple sentence. I.e. starting from that you can derive other consequences. E.g. "how the energy required for an object with mass to approximate the speed of light in spacial dimensions goes to infinity" is actually a direct consequence of that statement: every amount of energy you push into an object with mass causes it to accelerate, but due to the essential "clock speed of the universe", that acceleration is less and less as you approach the speed of light, and thus it takes an infinite amount of energy to reach the speed of light. Another way to think of it is that if it took anything less than an infinite amount of energy to reach the speed of light, then the speed of light couldn't be the universal speed limit, because you could add more energy that would accelerate it further.

On the other hand, my understanding is that quantum mechanics is another beast entirely, and one of the biggest problems in physics, and to developing a "theory of everything", is to unify quantum mechanics with general relativity.