If we are to understand the question in the historical sense, then we can’t know in a robustly warranted way. The lines of evidence are too weak to settle the matter.
What is a Christian to do?
Yet, it seems that what is important about the resurrection of Jesus of Nazareth in Christianity isn’t that he actually rose from the dead – it’s rather the significance of this for Christians. What is the significance?
The basic idea seems to be that, in rising from the dead, Jesus in some way conquered the power of death.
This is a separate question from whether death has been conquered. For, it could be that death has been conquered, but it has been achieved without Jesus resurrecting. At the same time, it is not at all clear within Christianity why God would take the form of a human and then die in order to conquer death (or whether this in some sense would be required).
Why is conquering death important in a practical sense? Because it implies the possibility of Heaven for humans, and therefore requires re-thinking how one lives – of focusing on not just the consequences of actions for now but in Heaven or Hell. So, as far as this goes, it’s not that Jesus resurrected, but rather the existence of Heaven that is central to Christianity.
Yet, many people insist that the historical question of Jesus of Nazareth’s resurrection is central to Christianity. Given the considerations above, why would this be so?
The answer seems to be evidential. That is, some people think that we know there is a Heaven because Jesus resurrected. Therefore, this line of thinking goes, the historical claim is central to Christianity.
Yet, as suggested above, it doesn’t seem that the historical claim of Jesus resurrecting a) entails the existence of Heaven (Jesus could resurrect without there being a Heaven, and vice versa, there could be a Heaven without Jesus resurrecting, it seems), or, more importantly, b) is the only way to know that there is a Heaven. Indeed, one of the central religious experiences in Christianity leaves the experiencer with a knowledge that there is a God, and that there is a Heaven one can get to.
If one has other evidential bases for believing there is a Heaven, then it seems the historical question of Jesus’ resurrection becomes less central. Rather, instead of being the evidential basis, in that case it fits into what one already believes, and so has a kind of synergy, but isn’t necessary. Indeed, in this case, in importance it can come to be thought of as primarily symbolic or mnemonic – a tool for thinking about or remembering key truths about Heaven.
If this is the case, then one can take what is central about the idea of Jesus’ resurrection – that there is a possible Heaven for humans – and make the experiences (which occur nowadays) which support this notion closer to the basis of a kind of Christianity, instead of the historical claim, which it seems is difficult to know in a robustly warranted way. This would make Christianity more evidentially robust – the trade-off being a dilution of its historical focus. I.e., an emphasis on the living Christ instead of presumed historical claims about Jesus of Nazareth’s life.