For a man who has spent his life traversing the planet pursuing the divine, Huston Smith’s world has grown rather small.

A devout Christian, Smith pioneered the field of comparative religion, having written “The World’s Religions,” first published 50 years ago and still considered one of the best texts on the subject.

Now 90 and suffering from osteoporosis, the famed religion scholar lives in a Berkeley assisted-living facility. His room resembles a monk’s cell: single bed, portrait of a saint above it, a modest desk and two small bookshelves (“The Dialogues of Plato,” Augustine’s “Confessions” and the “Oxford English Dictionary” are among the volumes).

Smith sits in a comfy chair, his walker nearby. Also within easy reach is a copy of the Holy Bible –– labeled “Old Testament and New Testament” –– from which he reads daily, just as he has for much of the last nine decades.

He is polite to a fault, but for his Jewish guest, he makes sure to point out that the terminology “Old Testament” sparks his ire. He believes it denigrates Jews and Judaism.

“I am passionately against the word ‘Old Testament,’ ” says the still-boyish Smith, “because it implies not too subtly it is superceded. Wrong. Totally wrong. It is the Hebrew canon.”

Then, borrowing a line from the folksong “Where Have All the Flowers Gone,” he adds in a lilting baritone, “When will they ever learn?”

Since beginning his teaching career more than 60 years ago — he taught at MIT, Syracuse University and at U.C. Berkeley, where he served from 1983 until retiring in 1996 — Smith has devoted his life to helping others learn about and appreciate the world’s religions, great and small.

His latest book is an autobiography, “Tales of Wonder: Adventures Chasing the Divine.” Published last month, it’s a 209-page personal — and personable — account of Smith’s wild ride, growing up a missionary’s son in rural China, going on to high academic esteem, raising a family and exploring the world’s great religions.

Perhaps “exploring” is too tame a word. More accurately, Smith virtually adopted faiths. Always a Christian, he was for decades also a practicing Hindu, Buddhist and Muslim.

He is close with the Dalai Lama. He knew Mother Teresa, Martin Luther King Jr., Alan Watts, Aldous Huxley and many more spiritual thinkers. In 1996, Bill Moyers conducted a five-part interview with Smith, “The Wisdom of Faith,” which introduced him to a wider audience.

“He was a scholar of religion who wasn’t satisfied,” says Daniel Matt, a Berkeley Kabbalah scholar and Smith’s friend. “He wanted to delve deeply into each tradition, appreciating that religion is different from most objective fields of study. He managed to retain an innocence and a curiosity.”

Huston and his wife, Kendra, with Zen monks at a Japanese monastery in 1957. Below, Smith rides a rickshaw in 1960s India.

“I am, you might say, a hands-on devotee of the world’s great religions,” Smith says. “First reading their sacred books, then pilgrimages to the most knowledgeable human beings living out the traditions and apprenticing myself, and then taking on the practice.”

He didn’t stop there. Smith also delved deeply into the faith tradition of the Native American Onondaga Nation in New York. He once tripped with Timothy Leary, ingesting psychedelics, which Smith calls “entheogens,” meaning “ways into God.”

One great religion Smith did not adopt hands-on, at least to the degree he had the others, is Judaism. In fact, that religion figures hardly at all in his autobiography, and only marginally in most of his other volumes.

But Smith affirms he did find a way into Judaism — arguably, the best possible way for a non-Jew: the mishpoche. His eldest daughter, Karen, married a Jewish man, converted and raised her kids in a Jewish home.

How did Smith and his wife, Kendra, take the news that their daughter was converting?

“We felt fine,” he says. “I moved into an understanding of Judaism by way of my daughter, who opened the door for me. It was no surprise because she always dated Jewish young men. We asked her about that, and she said, ‘Well, they’re the most interesting.’ I can believe that.”

He enjoyed many Shabbats and seders around his daughter’s dinner table in San Rafael. “When we were gathered, our grandson, now a handsome young man, he would sing out, ‘Why is this night different from all other nights,’ ” Smith recalls.

“Often Kendra and I, driving back home, would say, ‘This is really strange. Christian ceremonies are solemn, but there was nothing solemn about this.’ The toasts flowed, the wine flowed. It was just joyous.”

He marvels at what he calls “the great mystery of how Jews are such a small streamlet in [world] history and yet have produced disproportionately great people who moved history ahead.”

He also has a few favorite Jewish jokes. He offers one up: “A Martian arrives on this planet. He sees a bagel and says, ‘That looks like it would go well with cream cheese.’ ”

The peripatetic Smith visited Israel often throughout his career. The first time was in 1957, a year after the Suez War that threatened the existence of the young Jewish state.

He and his wife waited in Istanbul for weeks to get travel visas, but they could not. So they crossed Jordan and took a taxi to the Israeli border. Their Arab cab driver warned the couple they were “leaving freedom,” but they passed into Israel anyway.

“We had a marvelous time,” Smith recalls. On that trip, the couple visited two kibbutzes, one Orthodox and the other Marxist.

“In the first one,” recalls Smith, “Kendra noticed there were guns by the [dining room] tables around the walls. She asked innocently, ‘Oh, do you hunt?’” Later, the guns’ true function became evident as Smith and his wife realized that the compound’s high fences and guard dogs were to protect against Arab marauders.

At that time, one popular custom in the kibbutz movement puzzled the couple: the practice of raising children communally, separate from their parents.

“It didn’t work,” Smith says. “The reason is really, when you think about it, each child wants to feel special. But if he or she is in communal raising, then he or she is not special. And children need to feel special.”

One of his most indelible memories of Jerusalem came at a Simchat Torah celebration. Smith joined in the procession and noticed that a man carrying a Torah scroll seemed to falter.

“He said, ‘I think I’m going to pass on this because I’m feeling a little tired.’ The man behind him said, ‘Oh, you’re feeling tired? You hold the Torah and I’ll carry you around.’ ”

Smith moved to assisted living last year when his wife could no longer manage his care. She still lives in their house in the north Berkeley hills (while he “slid down the hill,” as he puts it, to central Berkeley). She visits him often.

He writes in his autobiography that the adjustment was hard — for three days. Then he quickly adapted, accepting his infirmities and making the best of it. He tries to be of assistance to residents worse off then himself. Smith also enjoys kibitzing with the facility’s Chinese maintenance man — in Chinese, the language of his missionary childhood.

And he daily greets the Muslim woman who works in the dining hall with “salaam aleikum,” the traditional Islamic salutation meaning, “peace be upon you.”

In middle age, Smith spent a decade practicing Sufism, Islam’s brand of mysticism. He is well versed in the Koran and the Hadith, the collecting sayings of Mohammad, so he feels confident when he claims Jews have nothing to fear from Islam.

Quoting one of those Hadith, he says, “‘Had [Allah] the will, we could have made [humankind into] one people. As it is, it is better this way. So vie among yourselves in good works. In the end it will all be revealed to thee.’

“If the Muslims in question knew their faith,” he adds, “then Jews would have nothing to fear.”

Nevertheless, he concedes that extremists have hijacked Islam, just as has occurred periodically in Christianity, Hinduism and other religions throughout history. Nothing seems to make the soft-spoken Smith angrier.

“For those fundamentalists who insist that this or that is the way, I say to hell with them,” he thunders. “I’m saying that half as a curse, half as a prediction.”

Smith’s distress stems from an all-encompassing ecumenism, his conviction that the world’s great religions share a single essence. Yet he distinguishes between what he calls the exoteric and the esoteric.

He uses a simple walnut to illustrate his point.

“Its external is the shell, which protects the kernel,” he says. “We value walnuts for the kernel, but it’s wrong to denigrate the shells, because there couldn’t be any kernel without the shell. Esoterically, in their essences, the religions are identical. But exoterically, they are very different. Christianity is Trinitarian. Try Trinitarian on a Jew!”

Smith’s respect for the great religions is deep seated, for he doesn’t know them only through traditional scholarship. Mostly his knowledge came from plunging in: living in a Zen monastery in Japan to study Buddhism, dancing with Sufi dervishes in Tehran, becoming a Hindu yogi disciple in India.

Traditional scientific detachment never was Smith’s cup of tea. And that got him into trouble sometimes, especially at MIT, perhaps not the most warm and fuzzy institution in academia. His 15-year tenure there was spent in the analytic philosophy department.

“Those were not happy years,” he says. “I loved the students, but I couldn’t stand my colleagues in philosophy because they hated me. My colleagues ruled that I could not teach graduate students because I was teaching religion as well as philosophy. Religion, according to them, was atavistic superstition.”

At Syracuse University, and later at U.C. Berkeley, he settled into the religion departments, where he felt he belonged. Smith went on to write “Why Religion Matters” in 2001. It’s a ringing defense of faith tradition in a time when the gap between secularism and religious extremism grew ever wider.

Religion mattered to Smith, especially when he was tested as never before.

In 2002, Smith’s adult granddaughter Serena disappeared at sea, apparently a murder victim. The following year, his daughter Karen, the one who had converted to Judaism, died of cancer at age 50.

It was a double blow that devastated Smith and his family. In his autobiography, he describes a last conversation with his daughter, how she had been thinking about mitzvahs as angels.

“Those angels don’t vanish with the acts that brought them into being but live on,” he writes, “affecting the balance between good and evil in the world. I think of Karen’s whole life as a mitzvah.”

In his grief, Smith turned as always to his Christian faith for solace. He spends hours each day in prayer, study and meditation. But unlike many Christians, who view Judaism as a faith superceded by Jesus Christ, Smith credits Judaism for, well, everything.

“We got it all from [the Jews] as far as the essence is concerned,” he says. “Judaism has it all, but there’s one problem: It’s only for the chosen people. But it’s too good to be confined.”

He says Christianity was a way for the Jewish ethos to “break out of its shell.” The same pattern occurred, he says, with Hinduism. Restricted because of its entrenched caste system, the ethics of that faith went global once the Buddha came along. “Again,” he emphasizes, “the truths are so wonderful they ought not be confined to a certain people or ethnic group.”

In his way, Smith followed in his parents’ footsteps. He has been a missionary, touting the beneficence of the world’s great religious and pleading for peace on Earth.

Having crossed into his 10th decade on earth, he understands his time is short, but he seems fearless and faith-filled.

Rather than cite chapter and verse from the Bible to bolster that serenity, he cites a cornerstone of advanced physics: the Einstein-Podolsky-Rosen paradox of 1935.

Essentially, the famous thought experiment proved that the space-time-matter continuum — that is, everything in the universe — is of a singular substance. In other words: We are all one.

“There is no separation,” Smith says. “There is only identity. [Poet] Robert Frost said famously, ‘Something there is that does not love a wall.’ His point: Walls separate. The separation opens estrangement. We’re in this together.”

“Tales of Wonder: Adventures Chasing  the Divine” by Huston Smith with Jeffery Paine ($25.99, HarperOne, 209 pages)

photo|cathleen maclearie