(Peter Paul Rubens, “Saint Peter as Pope”, ca. 1611)
It is easy to conceive how God could give us an infallible Church, because He gave us an infallible Bible.
One who denies the infallibility of the Christian Church must contend for either of these two things:
(1) God is unable to preserve Christian doctrine without error throughout history by means of (in and of themselves, without His aid) fallen, imperfect, fallible men and an imperfect Church run by such men (i.e., sinners).
(2) God was, of course, able to do this if He chose to (being omnipotent), but He chose not to do so.
Basically my argument is a subtle variation of a reductio ad absurdum: an exercise in consistency of logic combined with data from revelation that Protestants and Catholics hold in common.
If we grant that God allows doctrinal error, how much error does He allow? That wasn't the view at the Council of Jerusalem (nor St. Paul's). Everything was quite certain then, and “seemed good to the Holy Spirit and to us” (Acts 15:28).
I appeal to the infallible, inspired Bible in my analogy, because most orthodox Christians throughout history have held a very high view of Scripture. God did that via sinful men, so the question becomes: “why should doctrine or creeds be any different?”
It’s a matter of trust in God and acceptance of what seems fairly obvious (at least to me) in Scripture; i.e., a matter of revelation, which exists apart from a necessary epistemological rationale. We accept what it says in faith. One could say it comes down to hermeneutics, too, since what I see in the Bible seems perfectly harmonious with an authoritative Church, preserved from error.
Existence of error — even error very widespread and continuous in one way or another — doesn't prove that error is absolutely universal. One of the big problems here is that we cannot solve this dispute by recourse to mere philosophy or history.
It requires faith: both in terms of a belief that God could and would protect His Church (whatever we deem that to be) from error, per the scriptural promises, and also in the notion that there is such a thing as orthodoxy, which can be authoritatively determined and adhered to. Both things are matters of faith, at bottom, not philosophy or legal-historical reasoning.
I contend that this was the approach of the apostles and the fathers. One can't know what doctrines are in error and which are true without some standard. If the standard becomes “myself,” then that is weighed down by a host of rather obvious difficulties.
If it is, rather, some Church or tradition, then one has to argue on other grounds as to why that Church or tradition is chosen over against others. Is it always “presumptuous” to dare to have a belief in an authoritative Church and to not be so fashionably uncertain: garnering respect from many for being “nuanced” and “sophisticated” and so on, because we haven't figured out the answer to the question, and come to believe that no answer can possibly be obtained?
Is such skepticism and agnosticism on ecclesiology the default position of Protestantism? I have argued that it comes down to a lack of faith on the Protestant's part.
I don't see that the Bible (particularly how St. Paul seems to approach dogma and tradition) gives us any indication that so much of the content of the Christian religion would be subjected to error, with a resulting inability of the common man (not historians and apologists) to determine what is true and what isn't. I think what we have, rather, is an after-the-fact bolstering of the inherent skeptical, counter-traditional elements within Protestantism.
Denominationalism has so greatly increased the necessary existence of error (every denominational contradiction proves that), that it has to now be justified, and rationales must be given for it, in order for any Protestant to maintain his adherence to the overall belief-system. This is a very fundamental issue.
If we reject the notion that one institutional Church exists which can be clearly identified and adhered to, the alternative is the adoption of the classically Protestant (non-biblical, non-patristic) notions of either an invisible church or (if there is any distinction) a “church” that is made up of a patchwork quilt of the sum totals of the arrivals at truth of individual groups on individual questions, all (ultimately) arbitrarily determined by individuals who are profoundly influenced by the particular group they happen to be involved in (usually by a non-rational choice: family background, ethnicity, national identity, etc.).
God can't control human beings like puppets, but it is easy to conceive how He could protect doctrine, because He has already done so in the Bible. And we see plenty of examples of sinners in the Bible, but we don't see the widespread Protestant assumption of an invisible church or de facto doctrinal relativism, or ecclesiological anarchy. Doctrines have no “free will” to dissent; they are simply true descriptions of metaphysical theological realities.
Nowhere in the Bible does God promise to make a man perfect. He says “Be ye perfect like your heavenly father,” but note, that is a command, not a promise, and we have to respond (with the aid of His grace). But He has made many promises about His Word and doctrine, and truth. If one believes those, then one must believe in some sort of content of how that applies to concrete reality. They mean something.
It’s not a matter of a priori reasoning, but of the fact of the Bible, preserved from error, even though written and compiled and canonized by fallible, sinful men.
The proposal of the infallible Church (guided and protected from doctrinal error by the Holy Spirit) flows from that as a direct analogy, and also (I would maintain) from several indications in that same infallible Bible. So it is simultaneously a biblical and analogical argument, but it doesn't involve a priori assumptions about what God would or wouldn't do, because it is based on something He both promised and produced (the Bible).