Where did the "existing matter" come from?
Let's start with something coherent. What does it mean to be conscious? Two basic attributes:
(1) Duration. It's ongoing.
(2) "Loudness" - that's the nature of experience.
Meaning it is an ongoing stream of experiences more or less distinct (loud and clear). When those sensations subside, therefore, it is called UNCONSCIOUSNESS. The duration (#1 above) has ended. By definition, then, consciousness is
temporal.
What does this imply? A first moment, because an inifinite regress into the past is logically incoherent. In fact, if an infinite amount of time had to transpire to reach today, today would still have not been reached.
Where did the "existing matter" come from?
That's like asking, Where did God come from? My claim is that reality, at the outset, was not properly called God, but it rather was a finite amount of matter which I refer to as the Totality (the totality of matter).
The first moment in time refers to the first motion/thought to occur in that Totality. This is like a fetus awakening in a womb. Gradually a piece of matter awakened to full consciousness - and that piece of matter is the person whom we now know as Yahweh. Later He fashionsed the universe, the angels, our bodies, and our souls, out of the leftover matter.
When I speak of the original matter, don't think in terms of inert matter, protons, neutrons, electrons - that's a later fabricated system on His part. Just think in terms of tangible, self-propelling matter. Propelled by what? Free will.
Free will implies self-propelling matter. For example suppose you punch me in the face. What moved your fist? Ordinary cause-effect? If so, I can't be angry with you. But if free will propelled that fist, now I have cause to be angry.
There is nothing magical ("supernatural") about God's power. His power is the same kind as yours - free will. He's just a lot bigger than we are.
Over billions of years effort (a minimum of 13 billion years as far as we know) He laboriously acquired enough knowledge to become the quintessential ruler of the Totality - the ultimate protector and peace-keeper. He became holy.
Incarnation? Cinch. Think of God as a large brain. He then extricates one cell of matter from it. Will that cell remain powerful? No. Will it retain all its former knowledge? No. It becomes weak and ignorant. And He could have further reduced it's knowledge by scrambling that matter (like scrambling someone's brains). Then He placed that material soul in Mary's womb, binding it to a zygote.