Christian eternal life makes sense when seen as a state of permanently finding ones own good nature. For the ancient church, this was more as a corporate affair. Augustine wrote of the saved City of God, and of the damned City of Man, but not much about individuals. There seems to have been no room, after Jesus lived, for the unbaptized to be spared Hell. I think this was maybe to protect the power of the church (with Jesus as head) to mediate grace.
This became more of an individual salvation during the Middle Ages (at least in Western Europe.) And over time, the church figured out individuals would allow themselves to be controlled to get it. The distortion can get bad enough that heaven becomes a kind of ultimate job promotion we are all angling for. Then it fails terribly.
As I recall, in the early modern period in Europe, there were a series of murders of children. The murders wanted to die, but not be damned for suicide. They thought they had found a loophole, so to speak. Kill a child, who was pure and should go to heaven anyway. Then confess before the gallows. You get the benefits of death, but without the damnation. It was enough of an issue that some areas of Germany changed the law so the death penalty no longer applied for killing children.