Huston Smith has devoted a lifetime to exploring how the peoples of the world worship - and sharing his findings with the rest of us.
His Religions of Man, a clear-headed exposition not only of Judaism, Christianity and Islam but also Taoism, Confucianism, Hinduism and Buddhism, has been a staple of college curricula since it was published in 1958. Subsequently revised as The World's Religions, with a chapter added on the faith systems of indigenous peoples, it has sold more than 2 million copies, launching countless readers on wide-ranging faith journeys.
As a professor at the Massachusetts Institute of Technology, Syracuse University and the University of California, Berkeley, he helped to promote the now widely appreciated belief that God has revealed himself in different ways to different peoples. His books on Buddhism, Islam and the Native American church, and his films on Hinduism, Tibetan Buddhism and Sufism, remain seminal.
In the words of Alan Wolfe, Smith remains "an enormously important figure" - and one whose work still is gaining value.
"He really is the person who really informed Americans about all the religions that exist outside their own borders," says Wolfe, the director of the Boisi Center for Religion and Public Life at Boston College. "Now, of course, those religions exist inside our borders, so it's even more important."
Taking the approach, controversial among some of his academic colleagues, of exploring religion from the inside - studying under the guidance, for example, of Buddhist, Hindu and Sufi masters - Smith always has refused to prioritize any single belief system. He has enjoyed friendships with thinkers and doers as disparate as Aldous Huxley, Saul Bellow, Thomas Merton, Joseph Campbell, Mother Teresa, Baba Ram Dass and the Dalai Lama. He has been equally comfortable practicing Hatha Yoga and praying in Arabic.
Now, at 86, he is sharing his own religion. In his most personal work yet, Smith argues for a faith that he believes could unify the divided adherents of one of the world's great religions, and help to restore the belief in the transcendent to what he believes is its rightful place in the world.
"My days are numbered," he says over the telephone from his home in Berkeley. "I felt it was time to come full circle and write a book about my own faith: Christianity."
In The Soul of Christianity, Smith, who was born to Methodist missionaries in China, where he lived his first 17 years, returns to the early church - the community of believers before the Great Schism of 1054 divided Catholic and Orthodox, before the Protestant Reformation of the 16th century further split the faith.
"First-millennium Christianity was the trunk of the tree from which all of the branches and leaves have sprung," he says. "There's no reason why any Christian cannot subscribe."