Summary: The resurrection of is only unbelievable if you refuse to look squarely at the evidence.
I’m fond of joking that I have my resurrection body already reserved, and it’s a size 8. Everyone always laughs. Of course I don’t know what it will look like - I may have feathers, or fins! But we all know, don’t we, that whatever resurrection is about it isn’t going to include bunions or backaches. We’re all pretty clear that we’re going to get a brand new model, straight off the show-room floor, and we don’t even have to have all the parts handy to trade in, either.
People used to be much more literal about the Gospel promises of resurrection, says Jacques Barzun in From Dawn to Decadence, the massive cultural history of the Western world that I am currently plowing through. The great 4th century theologian St. Augustine taught that even the hair and fingernails shed in this life would be restored in full - although invisibly - in the heavenly body. We moderns take the resurrection much more symbolically, and most people - even Christians - really believe in the immortality of the soul only. Because, you see, we know so much more about science nowadays. Did you know that there’s not a single cell in your body that’s more than 7 years old? Our bodies are part of the great intertwined ecosystem, with atoms and molecules that once made up our skin and blood recirculating through other lives, lives of grass and trees and mosquitos and the like. So how can it possibly make sense to think that somehow we take this package with us across the great divide?
And I am one of those who believe that we don’t take our current bodies with us. St. Paul says so, in fact, in his 2nd letter to the Corinthians... that when "the earthly tent we live in is destroyed, we have a building from God, a house not made with hands, eternal in the heavens." [2 Cor 5:1] So it’s quite Biblical not to believe you need to have all your bones assembled in one place in order to partake of "that great gettin’-up morning."
But some people - even some Christians - take the de-literalizing of the Gospel somewhat farther. They believe that the resurrection of Jesus Christ itself was only symbolic, metaphoric, spiritual. This group believes that the miracles recorded in the NT were for a simple, primitive people, people who didn’t understand the laws of cause and effect, people who didn’t understand that miracles just don’t happen. We know better, we modern, scientific, enlightened folks. Miracles can’t happen, therefore they didn’t happen. We can take the core meaning, they say, and discard the fairy tales. What was important for the apostles - and for us - to understand is that love is eternal, that love cannot be killed, that love has power beyond the grave. This is called "de-mythologizing" the Gospels. There’s something faintly embarrassing for this group of people about claiming to believe in something so inherently irrational as an actual bodily resurrection; sort of like believing in the Easter bunny but not as cute.
But what it boils down to is that the resurrection of Jesus Christ is unbelievable - and so they won’t believe it.