There are some counter-arguments that have been made against Aquinas and Aristotle's first mover argument concept, and most would be iterations of the claim that is arbitrary to assume that the universe cannot exist in a state of infinite regress.
This counter-argument has a certain plausibility, for, given any effect, we can easily conceive of an indefinite regress of causes, even as, for any number X, we can always imagine a larger number, say X + 1 or 2X. From the fact that we can conceive of something, however, it does not follow that it exists, or even that it can exist; and there is, I think, reason to believe that a series of causes with no beginning cannot exist.
In the spirit of scholastic philosophy, I reply with a distinction: though effects may and often do precede their causes in the order of knowing (ordo cognoscendi), yet causes always precede their effects in the order of being (ordo essendi); in other words, even though we are, due to our reliance on sense-perception, often more familiar with contingent natural phenomena than with the principles that cause them, yet the principles are what come first in reality. Therefore the idea of a regress of causes is just that, an idea, a pure figment (fictum) with only an objective reality. (In scholastic jargon, a thing is said to exist only objectively when it exists only as an object of thought.) What takes place in reality is not a regress of causes starting from a last effect, but a progress of effects starting from a first cause, which we call God.
Why one first cause, one ontological Principle of the universe and not many? I believe the key to answering this question, which has given me some trouble, is to observe that, when St. Thomas wrote of 'motion,' he had in mind something much more general than the mechanical motion of a Galileo or a Newton: "motion is nothing else than the reduction of something from potentiality to actuality." (This is why I have preferred to speak of 'causes' rather than 'movers' and 'effects' rather than things 'put in motion.') If, then, there were multiple first causes, there would be no first cause; for, since none of the principles would be able to produce the universe without the cooperation of the others, each would be in potentiality to the others in some way, but it is proper to a first cause to be not in potency, but in act—not to be caused, but to cause. If we insist on a multiplicity of first causes, they can only be the divine Attributes (e.g. Love, Justice, Mercy, Wisdom, Power, Peace), which have diverse and interweaving cosmic manifestations and thus appear different to us, but which are really one and the same self-subsisting divine Essence.
Let's assume, however, for the sake of argument, that there was a prime mover, or first cause. What else could we derive about the nature of the first cause from simply stating it existed? How can we go from "there was a first cause," to "this first cause sent their son to earth in order to allow humans to be forgiven for their sins?"
Another distinction: we must establish the fact of divine revelation before we can examine its content. That the Son of God came to shed His Most Precious Blood for our redemption pertains to the content of divine revelation and can therefore only be known by faith, but the existence of God and the bare facts concerning the life, death, and resurrection(!) of Jesus of Nazareth can be known by reason. This is the basis of the distinction between natural theology and apologetics, on one hand, and revealed theology on the other: the former tells us that God has revealed, the latter tells us what He has revealed and, ultimately, how we must respond to it. This is why the First Vatican Council defines divine faith thus:
This council was summoned by Pope Pius IX by the bull Aeterni Patris of 29 June 1868. The first session was held in St Peter’s basilica on 8 December 1869.
www.papalencyclicals.net
Vatican I said:
This faith, which is the beginning of human salvation, the catholic church professes to be a supernatural virtue, by means of which, with the grace of God inspiring and assisting us, we believe to be true what He has revealed, not because we perceive its intrinsic truth by the natural light of reason, but because of the authority of God himself, who makes the revelation and can neither deceive nor be deceived.
As Fr. George Sauvage explains in his excellent Catholic Encyclopedia article on "Fideism",
A philosophical term meaning a system of philosophy or an attitude of mind, which, denying the power of unaided human reason to reach certitude, affirms that the fundamental act of human knowledge consists in an act of faith, and the supreme criterion of certitude is authority
www.newadvent.org
Fr. Sauvage said:
authority, even the authority of God, cannot be the supreme criterion of certitude, and an act of faith cannot be the primary form of human knowledge. This authority, indeed, in order to be a motive of assent, must be previously acknowledged as being certainly valid; before we believe in a proposition as revealed by God, we must first know with certitude that God exists, that He reveals such and such a proposition, and that His teaching is worthy of assent, all of which questions can and must be ultimately decided only by an act of intellectual assent based on objective evidence.
In order to make an act of theological faith, then, we must examine the objective evidence. If this man, Jesus of Nazareth,
- claimed to be the Son of God,
- demonstrated mastery of nature by working abundant and awesome miracles,
- demonstrated mastery of history by fulfilling ancient prophecies down to the minutest detail,
- promulgated the most sublime doctrines that have ever been heard by human hears,
- manifested peerless sanctity to the point of being admired even by his bitterest enemies, and
- confirmed his doctrine, gave a most signal proof of his sanctity, consummated all prophecy, and conquered the very powers of nature through an act so magnificent and so outrageous that it still excites the warmest devotion and the fiercest opposition from people all over the world,
then, to ask again the question which Jesus asked the Twelve in Caesarea Philippi (cf. Matthew 16:15), who do you say he is?