Jim Holt in the New York Times Magazine:
If God is dead, does that mean we cannot survive our own deaths? Recent best-selling books against religion agree that immortality is a myth we ought to outgrow. But there are a few thinkers with unimpeachable scientific credentials who have been waving their arms and shouting: not so fast. Even without God, they say, we have reason to hope for — or possibly fear — an afterlife.
Curiously, the doctrine of immortality is more a pagan legacy than a religious one. The notion that each of us is essentially an immortal soul goes back to Plato. Whereas the body is a compound thing that eventually falls apart, Plato argued, the soul is simple and therefore imperishable. Contrast this view with that of the Bible. In the Old Testament there is little mention of an afterlife; the rewards and punishments invoked by Moses were to take place in this world, not the next one. Only near the beginning of the Christian era did one Jewish sect, the Pharisees, take the afterlife seriously, in the form of the resurrection of the body. The idea that “the dead shall be raised” was then brought into Christianity by St. Paul.
The Judeo-Christian version of immortality doesn’t work very well without God: who but a divine agent could miraculously reconstitute each of us after our death as a “spiritual body”? Plato’s version has no such need; since our platonic souls are simple and thus enduring, we are immortal by nature.