'He is risen' is the familiar greeting amongst Christians at Easter. The belief that Jesus died and came back to life is central to Christianity. In the New Testament, the Apostle Paul writing to the church in Corinth says that 'if Christ is not raised, then your faith is in vain'. So it is no surprise that when atheists such as C S Lewis set out to examine the evidence for Christianity, they started with the resurrection. After all, disprove the resurrection and you disprove Christianity. Yet in the case of Lewis this backfired, and he converted to Christianity.
So what of the evidence for and against this seemingly ridiculous claim?
First, there needs to be some cautions. The resurrection of Jesus cannot be proved in a scientific or philosophical sense. The main written sources are from the Bible so the independent assessor has to discount these for now as they are not unbiased documents. Finally, and most importantly, dead people do not come back to life. Christians understand this and are aware that they are claiming something that is frankly extraordinary - and that belief in this is a matter of faith.
We do know that Jesus almost certainly existed - there are some Jewish and Roman documents that confirm this- as well as refer to the fact that he was executed as a criminal. What happened next is more difficult. We know from later Roman documents that early Christians had the belief that Jesus died and came back to life but this seems extraordinary.
Hence over the years people have offered several other explanations
The Swoon theory - this theory suggests that Jesus did not die on the cross but passed out, was believed to be dead and thus buried. In the cool of the tomb Jesus came round and believed that he had returned to life. (although surely placing a much weakened body on a cold slab would speed up death rather than revive?) unfortunately this theory doesn't fully grasp the horrors of a Roman crucifixion and very significant blood loss. There is also some modern prejudice here in assuming that ancient people we’re incapable of understanding the difference between fainting and death. So this seems unlikely.
The Stolen body - clearly various groups had motive to steal the body. The disciples are the obvious candidates as this would strengthen the claims Jesus made. Yet these same men, and the women with them, then faced great persecution for preaching the message of a resurrected Jesus. Would they not then admit the lie under torture? Or perhaps the Romans stole the body to annoy the Jewish religious leaders or vice versa. But surely as the new Christian group grew, the Romans could then quell the revolt by producing the body.
The Wrong Tomb - alternatively the disciples went to an empty tomb by mistake, as then did everyone else. Yet presumably someone would have been able to point them to the right tomb. But it seems this did not happen. Everyone got excited or puzzled over the empty tomb and Jesus‘ body lay undisturbed in another nearby tomb.
So the rival theories that oppose the resurrection each have their issues. In terms of the case for resurrection, there are two pieces of evidence that are at least puzzling and warrant consideration.
The missing body: No one has produced a body and the easiest way to prove that someone is not alive is to produce a body. Various groups may have liked to produce a body: the Jewish religious leaders to kill off this new messianic movement, the Romans to restore order as Religious quarrels between various Jewish and Christian groups in Judea broke out. Yet the body of Jesus has not been produced.
The courage of the early followers: Christianity spread rapidly through the ancient world despite great persecution. The followers of Jesus were often willing to die for their belief that Jesus had risen from the dead. They were changed men. In the first generation of Christianity their number would have included those who were eyewitnesses to the events of Jesus’ life. If the resurrection had been some sort of hoax surely they would surely have cracked under the pressure of Roman torture. These early followers believed the resurrection and were willing to die for that belief.
Of course this doesn't prove the resurrection but the events around the death of Jesus and its aftermath are puzzling. As extraordinary as the Christian claims are, the alternative theories are equally problematic. And this has led many otherwise sane and reasonable people to think that there is something in this idea of the resurrection.