This is your assumption, and I am going to go along with it - in this thread. Let’s assume that this universe is not all there is. Let’s pretend that your “first something”, “prime whatever”, etc… type of argument was successful. What can be deduced from this assumption? Use your logic only. The only starting point is that the universe does not stand on its own right, that it was created. No reference to faith, revelation and such. No other auxiliary assumptions. What can you say about this creator?
All of the “first somethings” arguments revolve around the ideas of metaphysical perfection. I assume that you aren’t really interested in this aspect too much in this thread, and New Advent has a good article on these types of arguments:
newadvent.org/cathen/06612a.htm
So, we have deduced the existence of a self-existent, metaphysically perfect, and metaphysically infinite being. We can also observe the fact of our own existence as beings which are not self-existent, metaphysically perfect and metaphysically infinite.
Think about what this means. A perfect and self-existent being exists. This being does not need anything else and cannot benefit (or “increase in perfection”) from anything. This self-existent being needs nothing else, cannot be benefited or harmed by anything else, and cannot change in response to anything else. This being is perfectly self-contained and independent.
Despite this, we also clearly exist as limited contingent beings. We are not self-existent and unchangeable, so we must draw our existence from somewhere. All contingent existence must come from non contingent existence, so our own existence necessarily comes from the self-existent being, often called “God.”
This tells us something about the nature of this perfect being- it created us without any benefit to itself. This perfect being cannot benefit from us, yet created us anyway. This indicates a form of altruism on the part of the perfect being. This altruistic dynamic is called “goodness” by most people.
On occasion, atheists ask why God cannot be just experimenting with us, or using us for entertainment, or plotting evil things against us. The reason is simply this- God cannot gain knowledge or entertainment from us. God cannot be an “evil” God because God by necessity cannot benefit from us. All forms of evil we observe involve self-gain, so it is irrational to propose a hitherto unknown form of evil.
So, we have established the goodness of God. A good God would desire to make His will known to us- for creating us without any form of guidance would be irresponsible. So, it makes sense that God would use some medium of communication with us. Philosophy and science seem to be methods by which God could communicate his will to us. However, religion seems to be the most relevant method by which God would be communicating to us. We would expect the religion to have some sort of structure and authority to effectively proclaim and protect the message of this God.
Looking at different religions, Catholicism is the best fit for these criteria. The Church has an organized structure to deal to pragmatic problems. This central structure enables it to declare an official body of doctrine as the official communication of God. The Church has the structure to identify and nullify false representations of this message, such as when it removes theological teaching licenses. There is an official, clear, party line that Catholicism espouses and holds binding on all, much to the annoyance of her opponents.
In contrast, other religions lack this authority structure. Protestantism is based on private interpretation of ancient documents, which has led to 30,000 different denominations and interpretations of what the Bible actually says. Protestantism does not work in terms of providing a coherent body of official doctrine. Islam has no central authority, so there is no way to tell whether terrorists or moderates are correct in their understanding of Islam. Eastern philosophies tend to deny the law of non-contradiction, which makes them meaningless in every sense of the word. Judaism is tied to a specific ethnic group, and there is no reason to think that a good God would give his goodness only to a specific ethnicity.
Mormons are unique in having an authority structure similar to Catholicism. However, they have other problems, such as openly contradictory accounts of its founding moment (the First Vision), baseless historical claims (the early Americans), no credible historical ties to the actual person of Jesus, whoever he was, among other problems. From this analysis, we can conclude that the Catholic Church is the best explanation for what we know by reason.
From this rational acceptance of the Catholic Church as an explanation, we naturally accept the authority of the Church and then, and only then, accept the claims based only on this authority- such as the authority of the Bible.
I am briefly summarizing here. I could go greatly in depth on each point, and will do so if you want.
