I think we can be fairly certain the authors didn't know them. Rather, people who did know him were tasked with passing on his teachings accurately.
They aren't largely inconsistent. If I went down to the store, I could find two very different books on Kennedy.
The gospel authors were not writing modern biography, but ancient biography. Moreover, for the most part they weren't dealing with a story told about jesus. They were dealing with a store of teachings, parables, short narratives, etc told about him. Each gospel author took this material and put it into a narrative, including their own redactions. The overall narrative is imposed over these independent oral traditions.
Now, are there inconsistencies? Of course. But this was not only typical of ancient history, but modern as well. Certainly the gospels cohere more than they disagree, even John and the synoptics have a lot of agreement.
You are dealing with sources representing what was primarily and oral tradition, and even the written tradition was treated orally. In an short, pithy saying, verbatim transmission or close to it may be the norm. In a parable, certain details could alter, as long as the main thrust was the same. Events have more alteration, simply because they happen only once, and can be told from the beginning from multiple points of view.
The point is that none of these minor inconsistencies say anything against the historicity of Jesus.
So you are ok with canonical inconsistency, but not ok with Gnostic inconsistencies? ...I'll let that one go for now, since this isn't a discussion about Gnosticism.
If the Jewish community who had become newly anointed in Christ were left with carrying on his teachings by way of oral tradition, wouldn't it make sense that they also wrote the books? Why did this story have to travel to Greece before anything was put on papyrus? Jews are EXCELLENT record keepers. Why do we have no record of a Jewish printing of these texts? Do you think they are lost to bad fortune and time? We don't even have the "original" document, so it's hard to say, I imagine. But all the same, you would think that new Christian-Jews would have had first pick of what happened, and that they would have differed from the Greek miracles we see in these stories.
I remember that Freke and Gandy cite that no one else knew of Yeshua except those who wrote of professing the faith. We would only look to the Gospels in order to determine a historical Yeshua... but there's nothing else we CAN look at. There are no records of him in the Roman logs, and similarly, anyone who claimed to know him or knew of him was dead by the time the stories were written down... and I wonder if we can take this as fact if it's after the fact.
I don't know or really care if Yeshua was alive. Because to me, that's not the point. In all probability he was, but this is an interesting debate.
On the other hand, if Yeshua did live, perhaps it's the case that he didn't perform miracles like the Gospel authors suggest. There are many who in ancient Greece attributed special powers and miracles to those who had superior intelligence or understanding. It was said that Pythagoras could also walk on water... etc. (I read this somewhere... but I think it may have been from Gandy and Freke... if so, I'm sorry. It's a piece of trivia that stuck with me.)
So even if Yeshua had lived, I imagine the Jewish oral story and the Greek oral story would have vastly differed from what it is. Some of the miracles Yeshua performed were textbook Greek God. It seems that the text at the time was reaching out to fellow Greeks, hence the heavy reliance on neo-platonism. If Yeshua existed, what can we attribute to him? Can we separate the things that were just thrown into the story? How? What is important for us to understand about this story if miracles are attributed to Greek tradition?
(By the way, Kennedy has all kinds of conspiracy theories on his head... no wonder they're inconsistent
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