What about a material cause? Why have you discarded that?
It is not that I discard the hypothesis.
Rather I take the hypothesis you mention and look at it and examine it.
H1. Something composed of matter i.e. (material) brings into existence (causes) space-time, all matter and energy from nothing.
And I ask myself:
1. Is this hypothesis logically possible.
Well, it seems to me that H1 does not even pass the first test. It is not logically possible for something composed of matter to bring into existence, from nothing, all matter, all energy, and space-time itself.
So I stop there and review the other available hypotheses. Are they logically possible at least?
H2. Something not composed of matter i.e. (immaterial) brings into existence (causes) space-time, all matter and energy from nothing.
And I ask myself:
1. Is this hypothesis logically possible.
Well, it seems to me that H2 as opposed to H1, is at least logically possible. Affirming it entails no logical contradiction
Then I ask:
2. What am I to make of an immaterial cause? How could something not composed of matter create all matter?
In response I go back and ask myself:
Do I have any presuppositions that seemingly contradict this hypothesis that I may need to examine more closely as a result of having evidence that they may very well be false?
Well, I observe cause and effect relationships quite often in my experience, and of course these things happen in the natural world in which I exist. Whenever I observe an effect, I reasonably conclude that it happened because something caused it to happen. Since they happen in the natural world, I expect them to be the result of some efficient cause that itself is composed of matter or at least an efficient cause which endures through time and space.
Then I ask myself this question:
Is the coming into being of the universe ex nihilo analogous to the effects that I observe in the natural world on a daily basis? IOW, should I look at the coming into being of the universe ex nihilo the same way I look at say, the formation of a star?
The answer is yes and no!
While they are both analogous in the sense that we have a relationship between a cause and its effect i.e. the formation of a star (the effect) as a result of certain natural processes acting upon matter (the cause), I understand that they simply cannot be analogous when it comes to their nature. Why? Because natural processes acting upon matter cannot logically be viewed as a cause of anything if they do not exist in the first place!
So from this it is seen that I use inductive reasoning and logic to arrive at arguing for a particular hypothesis over another.