You misunderstand me. Even though the writers spell out the inside knowledge right on the first page of each of their accounts, the assumption that Jesus of Nazareth is not just a Messiah, but the Messiah, and that the following accounts are chronicles of his Great Work on Earth is inside knowledge. If you believe that, then the accounts are true, possibly even objectively true, depending on how true you want them to be. All of the narrative and a lot of the justifications for the actions of Jesus and his followers are predicated on the assumption that Jesus is God. That's the believer-specific inside knowledge.

For those who don't believe in the premise spelled out in the very beginning, then the objectivity and the truth value of the stuff that follows is not guaranteed. Furthermore, there may have been deliberate omissions and additions to the accounts to solidify the ideological position of the writers. Finally, depending on whether you believe or not, passages take on different interpretations and conclusions. If it's already an assumption that Jesus is God and does all of this out of the goodness of his heart and want to reconcile humanity from their sinful nature, then there's no way in hell Jesus is going to grasp at something as pedestrian as political and temporal power. From outside the belief structure, though, if Jesus isn't known to be God, then he's a guy with a philosophy that's gathering followers. And while he's said he has no interest in politics, his followers weren't necessarily so high-minded. Peter's impulse was to strike with his sword. Remove the God part, and you have a rabbi with a fairly popular philosophy, which could compete with the current institutional structure.