Well, now YOU are making an a priori argument that “no a posteriori argument can prove anything,” which you cannot know for certain without assuming it a priori.
How can we know for certain that experience can never be sufficient to prove something without merely assuming that it can’t. Perhaps an experience or set of them can be sufficient, there is no way to know that purely by past experiences, i.e., a posteriori .
You might insist that, but you can’t prove it merely by experience. That is precisely your contention, so unless you want to undermine your whole argument, you need to retract the “can never” implication of your statement.
Clearly, Paul says that the wisdom of the world “did not know him”, he doesn’t say, “The world through its wisdom CAN NEVER know him.” That would be your addition to Paul’s words.
Given that revelation and revelatory experiences have been part of the human experience, i.e., Christ’s crucifixion happened as part of human history and certain facts obtained, perhaps it is now, after the fact, possible to argue from human wisdom, based upon historical premises to the implications of what the crucifixion entails about God, his nature and his existence.
If all scientific knowledge IS currently provisional (an a posteriori claim), that does not entail all scientific knowledge is necessarily provisional nor that it will necessarily remain provisional forever. That would make your claim about human knowledge an a priori one.
Care to provide an infallible proof for that?