A bit of clarification. There was no matter involved in the Big Bang, only energy. A Huge, incomprehensible amount of energy that formed elementary particles of matter only after it cooled quite a bit. Matter and energy are interchangeable (E=mc^2), so a huge amount of energy will equal a relatively small amount of matter. This means the whole of the Universe as we know it, millions upon millions of galaxies, and hidden matter we cannot even detect yet, was produced from a single energy influx the size of the head of a pin. Nobody has an answer as to where or why this sudden influx of energy, from nothingness, occurred. Any response you get will be speculative, spiritual, or BS.
No time, or space, existed prior to the Big Bang, to the best of our knowledge. My personal belief is that God "created" the Universe. My reasons are as follows
Sudden existence of anything from literal nothingness suggest a higher power.
If this sudden influx of energy was random, accidental, then why and how were physical laws formed that caused the energy to coalesce into matter?
Why was that matter subject to more physical laws, gravity, strong and weak nuclear forces, etc, that caused the elementary element of Hydrogen to produce more complex elements?
This diversity of elements, present with water and energy has allowed life to not only begin, but to develope, adapt, and evolve into a great variety of creatures, even just on Earth. Who knows how much more diverse the Universe as a whole is?
Is it possible that it was all a random accident? I cannot say it was not. I can say I believe there was an intelligent design behind it. For Physical laws to exist, it seems logical that some entity wrote those laws. Otherwise, why should the Big Bang result in anything more than a great cosmic energy spill into nothingness?