Those who want to be nice about Christianity, or at least nice about the very early Christians (didn't it all go wrong with St Augustine? Or was it St Paul?), say that the either the disciples convinced themselves that Jesus rose from the dead, by some kind of group-hysteria, or else that their talk about his rising was purely spiritual. That is, he didn't actually rise (there was no 'conjuring trick with bones'), they just meant that he was alive in their hearts or something like that.
This explanation faces an impossible difficulty, however: we are told that the tomb was empty. We only have the Gospel writers' word for this, at this distance in time, of course, but it is interesting to see that the Evangelists are concerned to counter a story current when they were writing, that the body had been stolen from the tomb by the disciples.
Biblical critics like this kind of thing, and call it 'redactional embarrassment': if a source reveals something he doesn't like, that he needs to deny or explain away, then it is particularly good evidence that the writer didn't make it up.
Here it is: Matthew 28:11ff.
... behold some of the guards came into the city, and told the chief priests all things that had been done. And they being assembled together with the ancients, taking counsel, gave a great sum of money to the soldiers, Saying: Say you, His disciples came by night, and stole him away when we were asleep. And if the governor shall hear this, we will persuade him, and secure you. So they taking the money, did as they were taught: and this word was spread abroad among the Jews even unto this day.
The 'Jews', Jesus' opponents among the Judaean theological and political establishment, were telling this story, the early Christians didn't like it, it was not flattering, they did their best to deny it. What would have been easy to do, to show the story was false, would have been to lead people to the tomb, show that it was still sealed and guarded, or else show them that it had the body in it.
But they couldn't do this. And 'the Jews', the chief priests and the elders, they had the same problem, because rather than rely on a story about the disciples stealing the body, they would surely much rather have silenced talk of the Resurrection by producing the body. But they said that the disciples had stolen it, because they had to say something to explain the annoying fact, that despite their precautions the tomb was empty.
So the tomb was empty. The body had gone. And like the people of Jerusalem following that terrible Passover of 33AD, or whenever it was exactly, we have to decide whom to believe: the disciples or the establishment. For it is difficult to think of any other explanations apart from these two: the one given by the Evangelists, that Jesus had risen from the dead, and the one given by the Chief Priests, that the body had been stolen.
Now the important thing is just this. If the disciples had stolen the body, then they were clearly not under any sentimental illusion that Jesus had risen from the dead. And while they may have thought that Jesus' ideas could never die or something soupy like that, they were nevertheless clearly engaged in a deliberate conspiracy to deceive the public. On this story, they stole the body and claimed that he had risen: they stole the body in order to claim that he had risen in a physical sense, in the sense in which many Jews of the day expected to be raised up on the Day of Judgement.
Now it could be that they disciples' story is true: that Jesus really did rise from the dead, by a bare-faced act of divine power. But if that seems difficult to swallow - it must be said, it's not exactly easy to swallow - then we are left with the conclusion that they were a bunch of dishonest, scheming scoundrels, right from the very first - from before dawn on that first Easter Sunday.
Why am I seeking to destroy the comfortable middle ground? The space occupied by those who think that the early Christians, at least, were peaceful and do-gooding people with a message of inner harmony and kindness to strangers, even if their inspiration, the gentle Jesus of Nazareth, ended up (later, maybe, thanks to St Paul, or the Gospel of John) with exaggerated claims being made about him. The space occupied by those cultural allies of Christianity, who may be our last rampart against the secularist persecution.
But it's not me doing this, it is God: He arranged things like this. It is Jesus Himself who, throughout His earthly ministry, consistently destroyed the compromise position, who destroyed the tenability of fence-sitting. It is Jesus who forces us to a decision. Are we with Him or against Him? Will we die with Him, or crucify Him?
You can hide from this decision, but it will seek you out.