Of course, your question is -- where did that first energy come from? Fact is, no one knows. That is a HUGE question. IF the Big Bang is true, then all that energy came from nothing! Some would have you believe that it came from a "quantum fluxuation in a vacuum". Huh!?!?
"Huh!?!?" is exactly why you should pay a bit more attention to why this theory is accepted by the scientific community. Also there is commonly accepted theory about the condition of the universe before the big bang, we have no evidence so support anything yet.
When you get to this level, it makes far more sense that the energy was supplied by a Supreme Being outside the influence of our 3-dimensional universe. In this case, "God said, let there be light!" is an exact representation of the first influx of energy into this universe, and describes a "Big Bang" event as accurately as men 5000 years ago could understand.
An interesting thought, yes?
No, it does not make more sense. See, the thing about the universe before the big bang is it lacks physical evidence to be interpreted thus far, making it "unexplainable". When something cannot be explained, that's it, it CANNOT be explained. You cannot state you know the answer to something that cannot be explained, that's a contradiction, it like saying I can't explain this therefore I can explain it.