You could be wrong!

An exchange I had with a Catholic apologist (indeed, a sedevacantist!):

It is interesting in a context of how Reformed presuppositionalists and Calvinists criticize evidentialists for "reducing Christian faith to probability" (an example is James White's constant criticism of William Lane Craig on these basis).

i) James White is not my standard of comparison.

ii) There is, moreover, a difference between knowing the truth and proving the truth. Arguments may be probable.

But if there is really no infallible authority, than Christian faith is indeed reduced to probability - everything, including Trinity and Deity of Christ, are merely "more probable interpretation of Scripture", and the truthfulness of Christianity is merely "more probable" than Christianity being false.

i) God can and generally does foster saving faith by putting the elect in churches where they are indoctrinated in the true Gospel. The fact that arguments may be probable doesn't mean the providential process of inculcating Christian faith is probable. A reliable belief-forming process can produce true, warranted beliefs.

ii) Moreover, unless you think God punishes Christians for innocent mistakes, unless you think God punishes Christians for holding mistaken beliefs through no fault of their own, because they had to rely on their individual aptitude and the available evidence, there's nothing scandalous about the consequence you derive.

An atheist will say you push the problem on step back regarding authority of the Bible. It is based on your private judgment and you could be wrong.

No, an atheist won't say that. Rather, it's Catholic apologists who are hung-up on "private judgment". 

But that is begging the question. You assume that Trinity, penal substitution etc. are true and say that God will lead people to churches which teach that doctrine. Unitarians and Jehovah's Witness could say as much about their doctrines and their churches.

i) Competing opinions are not equivalent arguments. 

ii) You missed the point. I'm referring to simple Christians who lack the aptitude to defend their faith by reason and evidence. In their case, God fosters saving faith through social conditioning, by putting them in churches where they hear the true Gospel.

That doesn't mean knowing or proving the truth necessarily depends on finding a good church. To the contrary, Christian intellectuals can acquire that information independent of church attendance. And they have the aptitude to defend their beliefs. 

I find your responses wanting.

I find your objections wanting. Your approval is not my touchstone.