Sarah Young, a former missionary whose devotional prayers became a Christian publishing juggernaut, has died at age 77.

The author of "Jesus Calling," which has sold more than 40 million copies, died Thursday (Aug. 31) after struggling for years with chronic illness and Lyme Disease. News of the Nashville native's death, first reported by US magazine Christianity Today, came a day after Publisher's Weekly reported that the author's health was "rapidly failing."

"It has been a joy and an honour to have Sarah Young as part of our publishing family," Mark Schoenwald, president of HarperCollins Christian Publishing, said in marking her passing. "Sarah was a remarkable woman who deeply loved God. Her words have resonated with people from all walks of life, and the global impact of her work is unparalleled."

Her passing brought an end to a writing career that was as successful as it was unexpected.

After graduating from Wellesley College, Young, who also held graduate degrees from Tufts and Covenant Theological Seminary, travelled to Europe, where she visited the L'Abri community in Switzerland, run by Francis Schaeffer, an influential evangelical pastor and author. While there, she later recalled, Young had a conversation that led her to embrace Christianity.

She met her husband, Steve, while in seminary, and after the couple graduated in 1977, they became missionaries with Mission to the World, a missionary agency of the Presbyterian Church in America. They served first in Japan and later in Australia, where Young worked as a Christian counsellor.

The so-called "Satanic Panic" of the 1990s, when a rash of rumors about devil-worshipping cults spread across the country, inspired Young to begin writing a series of journal entries that would become "Jesus Calling." During her prayer time, Young later recalled that she would spend time listening to God and "jotting down what came to mind."

"Jesus Calling" was published in 2004 when Young was in her late 50s. After a modest beginning, the book became a huge hit — spawning a series of related products, including children's books, journals and podcasts. All told, the Jesus Calling brand had sold 45 million copies by July of 2023, according to Thomas Nelson, Young's publisher.

In August 2023, "Jesus Calling" ranked second on the bestseller list compiled by the Evangelical Christian Publisher's Association.

Notoriously publicity-shy, Young lived mostly in seclusion in her hometown of Nashville later in life, refusing to give in-person interviews and shunning the kind of social media and public appearances common to superstar authors. When "Jesus Calling" was first published in 2004, Young was living in Perth, Australia, and that remote location made it difficult to do publicity for the book, she told Religion News Service in a 2021 interview, conducted by email.

"Because of my isolated location and my chronic health issues, I've never been on a book tour," said Young, who returned to Nashville a decade ago due to her illness. "Though my name may be well known, my face is not."

Written as if Jesus were speaking to the reader, Young's books have been controversial at times. She told The New York Times in 2013 that she did not consider herself a prophet, nor did she consider "Jesus Calling" a new book of Scripture. "I agree that revelation has ceased in the sense that the Bible is complete," Young told the Times in a written response to questions. "However, what I am doing is devotional writing, and I do so by asking Jesus to guide my mind as I spend time with Him — to help me think His thoughts."

In 2021, she told RNS that her books also point people to the Bible.

"My books tend to speak to different people in different ways, meeting them right where they are," she said. "I think that's because the books help people connect with Jesus, and He meets us right where we are. The books are designed to help people connect not only with Jesus, the living Word, but also with the Bible, the written Word."

Young told RNS that she'd often heard from readers about how "Jesus Calling" helped them draw closer to God, brought them comfort in times of illness and grief or gave them courage in the midst of their struggles.

Her success came with a great deal of responsibility.

"Becoming a bestselling author has meant that I have a lot more people to pray for than I did at first!" she told RNS. "And that has motivated me to pray at length every day for readers of all my books. I consider this a sacred responsibility and a delightful privilege."

Young is survived by her husband, Steve, two children and six grandchildren.

A memorial service for Young is planned for Christ Presbyterian Church in Nashville on Sept. 9.