In November 2019 John Chau made a final entry in his diary. “I think I could be more useful alive,” he wrote. “But to you, God, I give all the glory of whatever happens.” Within hours he was dead. He was 26. Despite repeated warnings from the people of North Sentinel, in the Indian Ocean, to stay away, Chau, an evangelical Christian, was determined to bring the gospel to the island’s estimated population of about 150, an “uncontacted” tribe. At least one of them shot the unwanted interloper with an arrow. The incident made headlines around the world. The Mission,...