Madeleine L’Engle, the author of “A Wrinkle in Time,” resisted labels. Her books weren’t for children, she said. They were for people. Devoted to religious study, she bristled when called a Christian writer. And though some of her books had political themes, she wasn’t known to write overtly about politics. That is, until her granddaughter, Charlotte Jones Voiklis, came across an unknown three-page passage that was cut before publication.

The passage, which Ms. Voiklis shared with The Wall Street Journal so it could be published...