Heaven and Hell: A History of the Afterlife - Bart D. Ehrman
The renowned New Testament scholar looks at the origins of the idea of Heaven and Hell, from the ancient Greek philosophers and the Jewish authors of the Old Testament, to the teachings of Jesus himself and, finally, the Christian theologians who followed.
It's a fascinating book, really easy to read and understand, with Ehrman carefully teasing out subtexts and hidden meanings from the literal words.
He discusses the ancient Greek belief in the soul, which is connected to the body while the person is alive, and which lives on after death. Writers like Homer believed it was a 'finer' (my word) version of the body, almost ghost-like, but enabling the dead person to still experience all of their senses. After death, the soul resided in Hades, which was kind of bleak and boring, but wasn't suffering eternal torment.
Later Greek thinkers, such as Plato, grappled with the notion of divine judgement, with justice being meted out depending whether a person had been good or bad during their life. For him, the soul was eternal. But others, such as Epicurus, despite subscribing to the notion of the soul, thought that it dissolved upon death, and that there was no continuity of consciousness when a person died.
The Jews of the Old Testament era, initially having an Epicurean kind of stance on the afterlife ('Sheol' is often cited as the Hebrew version of the Underworld, but it is also used frequently as the word for a grave or a pit; either way, it was not a place of eternal damnation), are greatly influenced by Greek culture later on (after all, Alexander the Great conquered the known world).
In fact, by the time of Jesus, there isn't a Jewish consensus on the afterlife or the soul: the Pharisees believed in the resurrection of the dead and some form of afterlife with rewards and punishments; the Sadducees generally rejected the idea of resurrection and the immortality of the soul, focusing on the here and now; and the Essenes, according to the historian Josephus, held a more Greek view, believing in the immortality of the soul which would be liberated from the body at death.
Jesus himself preached that his kingdom was earthly and was imminent (he told his disciples that he would return before some of them had died). He didn't talk about disembodied souls rising up to Heaven; rather, believers would rise from the dead and join him in Paradise on Earth. Non-believers and the wicked would be obliterated (ie: cease to exist).
The gospel writers, 2-3 generations after Jesus's death, and dealing with the fact that he hadn't actually returned, were faced with a dilemma, and moved the goalposts somewhat. To a greater or lesser extent, they still ascribed to an Earthly Kingdom which Jesus would rule over, but their different takes on Jesus's life and teachings paved the way for early church leaders and thinkers to put words in Jesus's mouth that he didn't say.
These people develop ideas of the afterlife that contradicted those of Jesus, and it's their teachings, not his, which carried over to the present day. It was they who posited the notion of Heaven being a place of eternal bliss and Hell as a place of everlasting torment.
I could go on. For example, Ehrman talks about early Christian martyrs willingly dying in the most horrific ways in order to mimic the suffering Jesus went through on the cross. And he expounds upon early Christian thinkers' concepts of Heaven and Hell as having different 'levels' or 'areas' where different things were happening to souls depending on how they lived on Earth, which influenced the likes of Dante more than a thousand years later. All the while, he makes it accessible and entertaining (if that's the right word?)
Anyway, in summary, it really is a great book and I highly recommend it.