It’s Thursday night at the smartest party in town and we are sitting over a drink talking about kids; Madonna, Demi and me. Life has some surreal moments to offer and this is definitely one of them. We’re having to raise our voices above the hubbub of beautiful people, including Gwyneth Paltrow and the fashion designers Donatella Versace and Valentino, gathered upstairs at Home House, a private club.

We are all here to celebrate — if that’s the right word — the launch of Becoming Like God, a book about the teachings of Kabbalah, an obscure offshoot of Judaism. Madonna is wearing the red string bracelet that denotes adherents next to a big, diamond-studded watch.

Demi Moore, a fellow Kabbalah-ist, is officially hosting the evening but it is really Madonna’s night. The former Material Girl has approved the venue, the guest list and the admission of a single journalist — me — to witness the wonders of ersatz spiritualism.

Kabbalah is regarded by some as worryingly near to a cult and earlier this year the chief rabbi’s office issued a statement distancing it from mainstream Judaism. A member of Rabbi Sacks’s cabinet said that there was “a great deal of unease about (Kabbalah’s) methods and the pressure brought to bear on those they view as being vulnerable and as possible sources of income”.

There have been similar warnings about other sects, but doubts about Kabbalah have been tempered in the public mind by the enthusiastic endorsement of glitzy celebrities. Fervent followers include Roseanne Barr and Elizabeth Taylor. Jerry Hall and Mick Jagger also had a flirtation with Kabbalah and hosted a fundraising dinner in London four years ago.

The book outlining Kabbalah’s theories seems more flaky than sinister, full of psychobabble about “transformative sharing” and getting rid of your “ego nature”. Certain sections are printed IN SHOCKING PINK CAPITAL LETTERS for emphasis, giving it a disturbing resemblance to the letters that journalists routinely receive from crazies in coloured, usually green, ink.

Rabbi Michael Berg, its author, is a pleasant chubby man wearing a little black beret. When I tell him that I find the design very arresting, he has the grace to look sheepish. “Oh, the pink was Madonna’s idea,” he says.

Madonna, who recently announced that she wanted to be known by her spiritual name Esther (although everyone on Thursday night continued to refer to her as Madonna), first got involved nine years ago. She was far from the needy, emotionally damaged wreck who we usually think of as finding refuge in obscure religions.

“I was what you would call at the top of my world,” she says. “I’d won a Golden Globe for Evita, I was pregnant, I had fame, I had fortune, everything that you would perceive a person would want in life. But I’m sure everyone’s had that out-of-body experience where you say to yourself — and it might happen at 28 or 38 or 68 — why am I here? Why am I inside of this body? What am I doing? And I was hearing that question a lot.”

A girl she bumped into at a party told her that she had been studying Kabbalah. “I love taking classes,” says Madonna. “I learn languages, I go to dance class, I love the idea of being in school. So I thought, ‘Okay, I’ll try this’. I went to a class and, yes, there was a man standing at the front who looked like a rabbi but what he was saying was amazing.

“I felt so inspired when I left the room. One thing Kabbalah teaches you is that your true potential in the world has nothing to do with selling records or making money or being popular, it has to do with what you are doing to help. What are you doing to make the world a better place?” The Kabbalah centre in Los Angeles was founded by Rabbi Rav Berg, father to both Michael Berg and the modern Kabbalah movement. Kabbalah, Hebrew for “received tradition”, is based around the Zohar, or Book of Splendour, a 2,000-year-old book in 23 volumes written in Aramaic.

Berg formulated a simple, practical version of Kabbalah that promises “fulfilment in every aspect of your life: relationships, business, health and more”. It was Kabbalah’s lucky day when Madonna arrived at the centre. Her huge popularity turned a little-known movement into a global brand. It now has 56 centres around the world and its website gets 150,000 hits a month.

Adherents can buy Kabbalah merchandise, from the £25 bracelets to bottles of specially blessed mineral water (very effective, apparently, in treating Madonna’s husband Guy Ritchie’s verrucas). It is just this sort of thing that raises hackles, but Madonna dismisses the criticisms with an imperious wave: “You know, I’ve been dealing with cynicism all my life.”