Paul does not seem to behave like an ENTP at all. He is also much more thorough in his arguments. ENTPs typically would rather engage people and NOT sit around and write out long theological expositions about their thought process.
Well some of the letters were written while he was in jail, so what else is he going to do?

Others were written as responses to questions that were asked. Ask an ENTP questions about something in which he is knowledgable, and he'll give you a mouthful.

Also NTP's in general are more thorough in their arguments compared to NTJ's. NTP's are better explainers in general, and they'll give you their whole thought process if you let them. NTJ's will often just give you the conclusion and may or may not explain why. (Also at least some of these letters are dictated, so Paul just had to "speak it" instead of "write it".)
(In fact, most of my e-mail exchanges with ENTPs usually involve them trying to spur further conversation by making provoking comments, NOT trying to "end conversation" as Paul does in virtually all of his writings. Paul seeks to offer convincing answers and conclusive doctrine, NOT provoke further conversation.)
Well that is email, which is a two-way discussion. When a letter takes weeks/months to be delivered it's not the same thing. Also there isn't a peer-to-peer context. He's the mentor explaining what to do. Try listening to an ENTP give a lecture or read on of their books to get a better idea of what they'd be like in this sort of context.
Paul's convictions do not seem to follow from his arguments. He presents his arguments for his theology... and then he applies it for the churches and readers so that they know how to use it appropriately. With Paul, I always get the impression he knows exactly what he believes to start with, and then finds ways to explain it (in Te style arguments) in ways that are convincing to his readership.
Well you have to put the writing in a format that the audience will understand (that requires Ne). He's not writing to scholars, so it's not going to look like the writings of some Renaissance philosopher. But it does follow an ENTP style of thinking. Theory -> Application. ENTP's are inventors of ideas, technology and procedures. Their normal mode of thinking is to take the theoretical and put it into application.
? I'm not sure what that has to do with things.
This was in response to your statement that conclusions can change over time. His basic message did not change, but it did grow (typical P fashion).
Each letter is separate, has a distinct purpose, is addressed to a distinct readership. each letter was appropriate to the context of the situation at hand.
True, but many of the same themes and ideas are often revisted. The later letters were longer and more thorough. He seems to be building and expounding upon his foundational ideas.
Also, just because Paul did not detail something at first doesn't mean he didn't already have the ideas in his head or his particular convictions about it to begin with. Romans is also longer because it's being addressed to pagans, correct -- not Jews? (Paul has to explain more to the non-Jews, who have more theological ground they must cover to follow what Paul is saying.)
All of his letters were written to churches outside of Israel. These typically had both Jews and Greeks, so in that respect the audiences for each of his letters are very similar (although culturally they may be different). Anyway...it's common for any type of NT to understate their details unless they are asked further. (All NT's are full of ideas and are also fully aware that most people don't want to hear all of the "why's".)
I'll give you that much, but I think it means little in the day and age that Paul lived. Perhaps if we were talking ISTx types, I'd think it meant more. But at that time, it was the only way to establish a church, wasn't it? There weren't phones. Letter delivery was long. Paul felt a burden to go everywhere. (I wouldn't call Jesus an ENTP by a far cry, as your style of argument could be used to make... yet he was even less stable than Paul.)
Jesus basically stayed in Palestine. Paul basically went all over the known world. Most of the other apostles traveled to far places, but they did not establish the sheer
quantity of churches that Paul did. Quantity is a defining extravert trait just as surely as quality is an introvert trait. Paul did not stay with a church to make sure it was established exactly the way he wanted (like an INTJ would). He cut and run as soon as he thought he could (like an ENTP would).
Would he? Would he have to, in that culture? Again, nowadays, we have the resources where people can sit around and plan something out and have others carry out their ideas.
INTJ's are planners. Regardless of era or culture, INTJ's are planners. A INTJ 2000 years ago may not write down all the details, but they do come up with plans with a definite ending. They are J's and J's desire closure.
Paul was not in that position. His world did not allow for it. He was (1) trained more deeply in Judaism than any of the disciples, (2) had supposedly seen Jesus directly and been given this vision to establish the churches, and (3) he had all of the answers. I can easily see an INTJ who feels like he and only he has the clearest vision to take it upon himself to go around to all the churches and make sure they were established; he was the "answer man." All of the churches were asking for HIS opinions.
I think any NT in this postion would do the same (well maybe not INTP, but the other 3 would). Each one would have a different style though. NTJ's would devise a plan and try to follow through. An ENTP would just grab a buddy and head west and then see what happens. That is what Paul did.
I don't see these points as exclusive of ENTP as expressed to the degree that Paul showed them. In fact, Paul had a clarity of purpose that is NOT typical of ENTP. He seemed to be very sure of himself and where he was going and what he was supposed to do. This is either a divine burden or an intrinsic part of his personality.
INTJ's can adapt faster than other J's, but they do not adapt faster than an ENxP. In some cases Paul just stayed in a city for a few weeks, established a church and then left. And this is in a variety of differnt cultures. That is the kind of adaptability that you really only see in an ENxP.
As for clarity of purpose, have you read the desciptions of ENP's? ENTP's are sometimes called "Visionaries" and ENFP's are "Inspirers". ENP's cast a vision and inspire people to want to follow it, without spelling out all of the fine details. This is basically what he did in each city that he set up a church. He'd proselytize in the synagogues in order to inspire people to believe in Jesus. He'd get the church started, and then let them fend for themselves expecting them to follow the vision he set. That's the ENTP style. The natural INTJ style is to develop a complete vision and see it through to the end.
I admit that ENP's do take longer than INJ's to develop their vision, but once they do then that (the paragraph above) is how they operate. Paul did spend several years in Antioch before his first "mission trip", so it fits with what you'd expect from an ENTP.
(all right, that was my best off-the-cuff pushback... So what have you got for me?

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How's that?
