But the lack of religious observance around him was frustrating enough to convince him to leave a decade ago.
"I felt that with all that openness, people were not committed to anything," he said.
When he returns this weekend to Berkeley to organize workshops for later this year and to deliver two book readings, Klein comes with what he calls a more tolerant attitude.
"That's been my journey of the past 10 years," he said last week in a phone interview from his home in Cambridge, Mass.
He still hopes that "as the years go by, all of us who have been so enamored by Kabbalah and Jewish meditation will come closer to halachah [Jewish law], which is the meat and potatoes of Judaism."
But Klein believes he has found a balance between his need for observance and his desire to be open-minded.
"It's the realization that the liberal communities are the ones more interested in Kabbalah," Klein said. "I've realized there are beautiful Jews everywhere."
He also hopes to reconnect with the Renewal movement, which he said has done more to support the study of Jewish mysticism and meditation than the other movements.
Klein first describes himself as "progressive Orthodox," which is more liberal than modern Orthodox — "if you can imagine that." He later describes himself as a "transdenominational" Jew.
His life certainly reflects his attitude.
Right now, the 45-year-old rabbi teaches continuing-education classes in Boston at the Hebrew College, which offers undergraduate and graduate degrees in Jewish education and Jewish studies.
He also is a guest rabbi at a Conservative synagogue's traditional minyan.
At the same time, he is coming to the Bay Area to promote "Meetings with Remarkable Souls: Legends of the Baal Shem Tov," his 1995 collection of spiritual, mystical folklore about the founder of Chassidism.
This year, his second book is due out. Klein hopes that "The Tree is Alive!: Early Kabbalah of Rabbi Isaac Luria" will be a "reader-friendly" guide to the complex teachings of the founder of Lurianic Kabbalism.
Klein's path is definitely one devoted to searching.
The son of an Orthodox rabbi, he grew up in the yeshiva world. Before his bar mitzvah, his family moved to Brooklyn and he was drawn to Chassidism.
In the early 1970s, Klein worked for a few months in San Francisco at Renewal Rabbi Shlomo Carlebach's House of Love and Prayer — an early institution in the Renewal movement. Klein particularly loved Carlebach's enthusiastic singing and acceptance of Jews from all walks of life.
He also studied with Aryeh Kaplan, a renowned Orthodox rabbi and kabbalist.
After Kaplan's death at age 48 in 1983, Klein looked for a new path. From his earlier experiences, he decided the Bay Area would be fertile ground for teaching Kabbalah and meditation. So that year he moved to Berkeley.
"There was very little receptivity on the East Coast toward Kabbalah at that time."
He began teaching at Lehrhaus Judaica and other Bay Area venues. He got involved in the Aquarian Minyan, Congregation Beth Israel, Chabad and Hillel.
Over time, however, he began to struggle with the fact that so few of his students observed Jewish law. The more involved he became in Kabbalah, the more connected he became to Jewish practice.
Traditionally, he said, "kabbalists were the most stringent of the Orthodox world."
So he headed back to the East Coast in 1988. But he has found the observant world isn't perfect either.
Though the Orthodox are regarded as the guardians of the Kabbalah, Klein asserts they generally scorn Jewish mysticism.
In the Orthodox world, he said, one is supposed to publish and buy Kabbalistic texts — but not study them. The attitude springs from "Shabbetaian disaster," Klein said.
That's a reference to Shabbetai Tzevi, a 17th-century kabbalist with a large following of Jews who believed he was the messiah. He later converted to Islam. Even today when someone does something strange, Klein said, Orthodox Jews might ask: "Is he a Shabbetai Tzevi-nik?"
In addition, he said, the post-Holocaust world of traditional Judaism is fixated on rebuilding the community to prewar numbers.
A key phrase in Kabbalah is tikkun haneshama, or repairing the soul. The Orthodox world, he said, is still focused heavily on tikkun hador, or repairing the generation.
"This is where they veer away from Kabbalah, which is highly individualistic," Klein said. Rebuilding a generation "is not a mystical thing."