Have you read Catholic historians on these periods in history, or even historians without an axe to grind?
Replying on all points at once might be counterproductive, but maybe I can start a conversation on this one.
In some sense, I don’t merely believe in the existence of God anymore; it’s something I know. But neither is it something I became convinced of because I read a quick proof of it somewhere. It took time to develop the philosophical insights that led to this conviction. Let me point you in a direction I found helpful.
First, here is a thought experiment. Imagine you wake up in a locked room, with no recollection of how you got there. As you look around the room, you see no apparent door or visible window. Imagine the space and furniture as you’d like. Eventually, something strikes you: you can see, so there is light in the room, but you don’t know where the light is coming from. So you set out to find a source of light. How might you do that? You look more closely at everything. Maybe you make a little cave with your joined hands, and you peek in with an eyeball. If it’s dark then the light originates from somewhere else. And you must keep looking to find the source of light!
Arriving at the conclusion that God exists is a somewhat similar process. While there are many aspects of the world that speak to the existence of God, the very being of things is perhaps the most revealing. When you wake up in the morning, consider that things exist: you, your bed, whatever else. Ask each of the things in your environment: Why do you exist now? Are you the source of existence or do you get your existence from another? A closer consideration of the existing things of the world shows that they don’t exist necessarily: what they are does not tell us whether they are. They might not have been. But things do exist, and so there must be some source of being that exists necessarily, that has being by itself and communicates it to others, in the manner of a source of light.
I have found that materialistic atheists have two kinds of attitude towards this line of argumentation - and towards the question of God in general.
Firstly, the question is thought to be unscientific and therefore not a genuine question. A fortiori, the line of argumentation is thought to be unscientific and therefore non-rational. I can hear Popper’s name echoing in the void… My first, short response is that the scientific methods are not reducible to falsifiability, and human rationality is not reducible to the methods of this or that science.
If pressed further, another attitude sometimes emerges, no longer skeptical but daringly metaphysical: the universe is just the way it is and doesn’t need further explanation. At bottom, it has its own necessity that doesn’t need any further ground of existence. The accounts may vary. Before Father Lemaître proposed the primeval atom (mocked by his atheist peers under the now better known name of “Big Bang” theory), cosmologists believed in a stagnant cosmos. Since then, quantum-physics-inspired accounts have been proposed for the emergence of the world, always bringing back contingent existence to some kind of necessary substratum - or a “nothing” that is really not nothing at all. But whatever their scientific merits, these explanations are not compatible with atheism in the strict sense. A necessary being as the ground of existence is what is we call God (it’s a good starter definition for what we mean by the word “God”). Whether it’s described as space-time, or higher dimensional branes, or a wave-function doesn’t really change its basic ontological status.
I take the last point to be a hint that genuine rationality must acknowledge the existence of God – the alternatives are God or fundamental absurdity – and we do philosophical theology best when we are explicit that that is what we are doing.
Here is the way St. Thomas Aquinas rehearses one version of the argument I summarized before:
“Now, whatever belongs to a thing is either caused by the principles of its nature, as the ability to laugh in man, or comes to it from some extrinsic principle, as light in the air from the influence of the sun. But it cannot be that the existence of a thing is caused by the form or quiddity of that thing ─ I say caused as by an efficient cause ─ because then something would be its own cause, and would bring itself into existence, which is impossible. It is therefore necessary that every such thing, the existence of which is other than its nature, have its existence from some other thing. And because every thing which exists by virtue of another is led back, as to its first cause, to that which exists by virtue of itself, it is necessary that there be some thing which is the cause of the existence of all things because it is existence alone. Otherwise, there would be an infinite regress among causes, since every thing which is not existence alone has a cause of its existence, as has been said. It is clear, therefore, that an intelligence is form and existence, and that it has existence from the First Being, which is existence alone. And this is the First Cause, which is God.” - St. Thomas Aquinas (De Ente c. 4)
