Man could not blame his weaknesses on ‘original sin,’ said Pelagius. “Everything good and everything evil . . . is done by us, not born with us.” Pelagian doctrine quickly became the talk of Christendom.

But not for long. Church leaders viewed this abandonment of ‘original sin’ as heresy. And Pelagius unwittingly played right into their hands by favoring what was by then a popular custom​—infant baptism. A bishop named Augustine saw this as a glaring inconsistency. ‘If infants must be baptized,’ argued Augustine, ‘what of those unbaptized?’ The seemingly logical conclusion was that such ones would suffer the fires of hell because they were unbaptized. This point apparently established, Augustine struck the fatal blow: Since unbaptized infants indeed suffered damnation, what else could account for this but ‘original sin’?