There is no possibility that Paul was illiterate.
He was a student of the famous rabbi Gamaliel, and one of the kings before whom he testifed (Festus?) said to him, "Paul, your GREAT LEARNING has made you mad."
Paul's family specifically sent him from Turkey to Jerusalem to study.
I'm not denying Paul (and Saul) were very smart, but there's no evidence that he knew how to write.
No one knew how to write back then except scibes...that was the whole point of being a scribe. If everyone could have written, there wouldn't have been scribes. So, perhaps "illiterate" is the wrong word (I'm sure he could read), but writing is a whole different matter.
I mean, look at monks, they were the people that had to copy texts for 1000 years because no one else knew how to write.
Again, nothing nasty intended...just a discussion.
"Paul's family specifically sent him from Turkey to Jerusalem to study"
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Turkey? No such place until the 1920s. But them again you knew that...