Passengers forced open the doors on a busy rush-hour train and climbed on to tracks after becoming “panicked” in the carriage.
It happened outside Wimbledon station in south-west London at 08:30 BST as a man apparently began reading lines aloud from the Bible.
Commuters became scared when the man also began saying “death is not the end”, a passenger said.
Rail power lines were cut as passengers “self-evacuated”, police said.
Trains on the route were disrupted for nearly 12 hours, but are now running normally.
Ian, who was on the train, said the man’s Bible-reading led to a “commotion” and a “crush”.
He said someone then asked the man to stop speaking “as he was scaring people” and “the guy stopped and stood there with his head down”.
The train had been travelling between Shepperton and London Waterloo. British Transport Police (BTP) said no arrests had been made.
A Network Rail spokesperson said no passengers or train staff were injured but “significant delays” would continue on services in and out of Waterloo.