This topic is a favorite of those who argue that Jesus is a mythic figure who never even existed, but I'm NOT approaching it from that angle. However, it's a genuine mystery that causes me to suspect that Jesus' ministry may have been quite different from the biblical portrayal.
The way the NT is organized, it's quite easy to be lulled into thinking that Paul was writing his epistles against the backdrop of the four Gospels. This is, of course, wildly incorrect. Paul wrote long before the Gospels were written and indeed died long before they were written (i.e., he is believed to have died in 62 AD vs. sometime after 70 AD as an early date for Mark, while some of the epistles are much earlier).
Yet Paul scarcely even mentions the historical Jesus. There is no mention of the Virgin Birth, Mary, the teachings and parables, the miracles or anything else that is central to the Gospels. (Paul does, of course, emphasize the Resurrection, but he doesn't mention the empty tomb.) On the other hand, the Resurrection appearance to more than 500, which Paul mentions in 1 Corinthians, is never mentioned in the Gospels - an extremely odd omission that I find as puzzling as Paul's omission of the historical Jesus.
It's believed that the Gospels arose out of eyewitness accounts, a carefully preserved oral tradition, and one or more "sayings" documents such as Q. Hence, the Gospel material was certainly available when Paul was writing, but he never mentions it.
It can be argued that Paul had other concerns, but this isn't really true. He repeatedly addresses hot-button issues in the churches and gives direction on Christian living to which Jesus' parables and teachings would have been directly relevant, yet he never mentions those teachings.
I recently did a study of just how tiny Judea was in Jesus' time. To give an idea, the entire territory of modern Israel, including the disputed territories, is approximately the same size as the Phoenix (Arizona) Metropolitan Area or the state of New Hampshire. The population of Jerusalem in Jesus' time is estimated at 60,000 to 80,000 with Judea estimated at 200,000 to 300,000 (these figures are scholarly estimates and there are estimates that are fantastically higher, but these are mainstream estimates). In any event, Jesus operated in quite a small area with quite a small population.
Does it seem plausible that, in an area of this size, an individual doing the things Jesus is described in the Gospels as having done would not have achieved FAR greater notice during His lifetime? Does it seem plausible that the Gospels would be almost entirely silent regarding the 30 or so years of His existence before He burst on the scene? Does it seem plausible that the Roman and Jewish historical records would barely even take notice of Him?
I see no plausible way to explain these things except to conclude that Jesus' ministry was most likely far more localized and obscure than the Gospels suggest and that it was the Resurrection that caused a certain degree of "mythologizing" to develop around the historical figure He actually had been. This is why I always take the position that Christianity stands or falls with the Resurrection and pretty much NOTHING else.
I don't believe that honestly addressing puzzles such as this is in any way heretical or blasphemous or even something God would discourage. Even the question as to whether Jesus existed at all is a perfectly legitimate one; the vast, vast majority of scholars, including secular scholars, believe that He did. On the other hand, I don't believe there is anything particularly pious, faithful or pleasing to God about pretending these puzzles don't exist or trying to explain them away with glib and facile "explanations" that really don't fit the facts.
