Everything we know about the facts of Jesus's life death and resurrection comes from the four canonical gospels.
That's not to say that the other NT writings don't mention these events, but Paul is much more concerned about the theological implications of the events rather than the details of what actually happened. For example, you'll never find from reading Paul anything about where Jesus was crucified, when this happened, who witnessed it, etc. Nothing that Paul says about the earthly Jesus is not mirrored and expanded in the gospels. Paul says that Jesus was 'born of a woman', but not which woman. For those details we need to turn to the gospels.
Apologists often make a great deal of the secular writings about Jesus, such as Tacitus, Seutonius and Josephus, but all of these date to times several decades after Jesus, and all of the information in them merely confirms that there were "Christians" at the time of writing, and don't really tell us anything about Jesus himself.
So. Everything comes back to the gospels. How reliable are the gospel documents? Can we trust them to contain history? Who wrote them and when? These are all important questions, and we may never know the answers to them all. I've already discussed the Synoptic Problem at length, so I don't need to go into that here. But here I'll go into a couple of other questions:
1. Did Jesus die on the cross?
The first thing to say about this is that all four canonical gospels agree on this point - Jesus was crucified and died. The problem faced by anyone trying to defend the theory that Jesus was crucified but survived is that they have to show that the gospel writers were correct in some facts and wrong in others. If the gospels got the plain fact that Jesus died wrong, then how can we believe anything else in the entire story? Jesus death is the central event in all four gospels, if he hadn't died, then there is no gospel. To the writers of these stories, Jesus life only makes sense in the context of his death. If we assume that the gospels are in any way reliable, then that leads us to the conclusion that the authors of these documents were utterly convinced that Jesus died on the cross.
I have to say that if you want to doubt the gospel writers belief in Jesus's death on the cross, you also have to doubt everything else they say about Jesus's life as well.
Did Jesus die on the cross?
- If we accept the testimony of the gospels, then yes.
- If we don't accept the testimony of the gospels, then we don't know.
- I'd say that there is no way to conclude 'no' based on the available evidence.
There is really no way to honestly use the gospels to conclude that Jesus - the man who taught in Galilee, had 12 disciples, performed miracles, and so on - did anything other than die on the cross.
Of course, using the same reasoning, we must conclude that - if the gospels are trustworthy - that Jesus also was raised from the dead (as attested in all four gospels) and appeared in physical form to his disciples after this (as attested in 3 out of the 4).
Its an all or nothing thing, as far as I can tell. And it probably works the other way around for most people - those who presuppose the death and resurrection of Jesus regard the gospels as trustworthy, those who presuppose the non-resurrection of Jesus must therefore regard all the information in the gospels as potentially untrustworthy. I can't really see a good case for the middle ground of accepting that the gospels got some details (such as the main topics in them!) wrong, but were otherwise accurate in terms of what they say about Jesus (his teaching, healings, etc.).
Now, I've come to the conclusion - in other posts - that the gospels do contain errors and misinformation, which - using the reasoning above - must lead me to the conclusion that we simply can't know whether or not Jesus died on the cross and was resurrected a few days afterwards.
The best I can conclude is that IF Jesus was crucified by the Romans, then there is an exceptionally high likelihood that he died on the cross, as history (Josephus) only records one survivor of crucifixion, and that only after being quickly taken down from the cross - a very rare event indeed.
The only thing we can really say with any certainty is that Christians in the late 1st or early 2nd century believed that Jesus was crucified, died and rose again, several decades before their time. This doesn't count as evidence one way or the other, I'm afraid.
2. The Gospels as History
I'm about to make the same point again, but in a different way.
As I see it, there are really only two options, and they don't start with the historicity of the gospels, they either end up there, or they don't. The starting point is the resurrection of Jesus.
IF Jesus was resurrected (raised from death in a physical and 'super-human' body) then the central beliefs of the Gospel writers are fundamentally true, and there is a good chance that the biographies of Christ that they wrote are grounded in reality and may contain useful historical details.
IF Jesus was not resurrected, then the apparent central beliefs of the Gospel writers are false and the Gospel writings are, at best, the writings of honest but gullible people who had been told a bunch of myths and believed them, or, at worst, complete and intentional fiction. In this case, there is no reason to suppose that any of the material in the gospels is good historical data.
Yes, I know that the gospels contain at least four secularly attested historical characters - Herod the Great, Herod Antipas, Pontius Pilate and Caiaphas the high priest. I would argue that these characters, while they do feature in the plot of the story, are more part of the setting of the gospels than integral to the story. In much the same way, Jerusalem and Galilee are part of the setting of the stories, the fact that we know there was a Jerusalem does not in any way provide evidence that the stories in the gospels which are recorded as happening in Jerusalem actually happened. There are numerous historically verifiable locations and characters in the stories of Sir Arthur Conan Doyle, but that doesn't imply that Sherlock Holmes was a real person, only that the stories about him were set in a real historical setting.
So where does this leave us? I think it means we can't use the internal evidence of the gospels to prove the resurrection of Jesus. Or the death of Jesus. Or even the life of Jesus.
Without external 'secular' evidence for the person of Jesus, not merely evidence that there were believers in Christ Jesus a generation or two after the alleged events, we really cannot be sure of anything to do with Jesus in history. Anything you want to claim about him (for example that he claimed to be the 'Son of God' or that he was an apocalyptic prophet, or that he was born of a virgin, or that he had 12 disciples) relies, primarily, on the assumption that he was resurrected from the dead. Without that fundamental assumption, we cannot 'know' anything at all about Jesus.