John Dominic Crossan closes the main text of his 1994 book Jesus: A Revolutionary Biography with the question: "How many years was Easter Sunday?" His conclusion: accounts of a literal, bodily Resurrection are not present until, at best, the very end of the first stratum of historical Jesus material (Mark, in the early 70's CE, roughly four decades after Jesus's death) and at worst not until the second. This means that it took at least that long for belief in a literal resurrection to become ingrained in Christianity, which suggests that it didn't actually happen.
You might be thinking that Paul, who is our earliest source for the life of Jesus, mentions the resurrection, and while that is correct, a careful reading shows that Paul is never referring to a bodily resurrection.
Understand that we are talking about Jesus the man; a man of flesh, "of dust," as Paul put it, a man just like anyone of us. Keeping that in mind, consider what Paul actually wrote about the risen Jesus, as well as what his student Luke wrote in the book of Acts, presumably from memory of things Paul had told him.
In 1st Corinthians, Paul counts his experience among many other experiences of the risen Christ to other disciples, implying no difference in the form of the experience, which he described to Luke as "a light from heaven" (Acts 9:3). Then in that same letter, he comments on the nature of the risen lord: "It is sown a natural body; it is raised a spiritual body." (1 Corinthians 15:44, emphasis mine). He continues to draw a sharp contrast between the natural and spiritual body, and then finishes by insisting "Just as we have borne the image of the man of dust, we shall also bear the image of the man of heaven." (15:49).
Paul experienced the risen Jesus both as a great light and as an audition, but not as a physical man. He implied that the rest of the resurrection appearances were of the same nature. He spoke of a spiritual body, distinct from the natural, physical body. It almost sounds as if, while certainly insisting upon the truth of the living Christ (as opposed to the crucified Jesus), Paul means something else than a walking corpse, an empty tomb.
Granted that all evidence of a literal bodily resurrection comes from later sources, and that I'm convinced belief in the supernatural is in no way a prerequisite to being a Christian or following Jesus, I submit that it is not only possible, but reasonable and quite possibly even correct to find meaning in Easter without believing that a man literally rose from the dead. Let me explain.
I have no problem saying "Christ is risen" (or Christos anesti when I'm with the Greek side of my family) when I celebrate Easter, but that is because I understand and hold in reverence the power of metaphor and parable. When I affirm the resurrection, it means not that I believe in lich Jesus (not zombie Jesus; never zombie Jesus), but rather that I believe in the living Christ; that is, that the transformational power of Jesus is still available to anyone who seeks it.
Of course, most Christians believe this (or something similar to it), but I submit that this idea is not just a Christian affirmation but the true meaning of Easter.
Rising from the dead is a legend, a miraculous deed, a magic trick. Whether or not it really happened, its numinous quality is derived from the conviction of the believer, just as prayer's effects on healing can be mostly chalked up to the placebo effect. That is not an indictment, by the way; whether you understand religion's positive effects scientifically or supernaturally, they work.
But what I'm talking about is a specific historical event and what came after. Jesus of Nazareth was crucified, and the magnificent (and dangerous) vision of the Kingdom of God that he taught was supposed to go with him.
But it didn't, and the answer to the question of why lies not in any miraculous deed, but in the genius of Jesus's program itself.
The Kingdom of God was never a religious domain meant to be led by Jesus (Jesus never claimed to be God), nor was it ever about Heaven. The Kingdom of God is a socio-political program of nonviolent resistance to the world's injustice that, mind-bogglingly, was created in one of humanity's most inhumane and unjust societies.
The Romans, led by Pilate, and the Jewish authorities (the chief priests, scribes, and the elders), led by Caiaphas, misunderstood Jesus's program at its most fundamental level. They understood that it was nonviolent; that is why Jesus's followers got away. But the men who crucified Jesus understood him against the matrix of apocalyptic expectation personified by Jesus's own mentor, John the Baptist.
But John was dead and God had done nothing. Jesus's thinking evolved, and he began a paradigm shift from expectant eschatology, where humanity waits for God's intervention, to collaborative subversion, where humanity fights against its own injustice in God's name. And this is an idea that is bigger than any one man, even the man that founded it.
That's what Easter is. Jesus may be dead, but his program lives on. Christ represents not a man, but an idea, and that idea cannot be killed, not by all the nails the Roman Empire could muster.
I'm not here to tell you that you're crazy or stupid for believing in the resurrection. I'm here to say that Easter belongs to each one of Jesus's followers, even if they don't believe in it literally.