It is evening prayers. In a small hall in Jerusalem, the service is being conducted in Hebrew. Some of the words - indeed some of the prayers - chime exactly with those of a synagogue prayer-book. But this is a Catholic Mass.

There are, it is estimated, more than one billion Catholics around the world. Within the Middle East, the great majority celebrate Mass in Arabic. A tiny sliver - about 400 - celebrate Mass in Hebrew.

Leading the service this evening is Father David Neuhaus. Hebrew, he says, has the distinction of being the first language, other than Greek or Latin, in which the Vatican allowed Mass to be said.

That was in 1956, almost a decade before the decision was taken to allow Mass to be celebrated in any language. The argument, from the petitioners to the Vatican, was that Hebrew was one of the three languages used to inscribe Jesus's cross.

A few days before conducting the evening Mass, Father Neuhaus relates his own, remarkable story in measured and thoughtful tones.

We are sitting in the garden of the Pontifical Biblical Institute, in the centre of Jerusalem - the end to a convoluted journey.

David Neuhaus's parents were German Jews who fled the Nazis and settled in South Africa. As that country descended deeper into the grim mire of apartheid, the teenaged David was sent to Israel, to continue his schooling. There he met a "powerful, mystical" Russian Orthodox nun, and he discovered Jesus.

"I had to then deal with what it meant for a Jew to join a Church which is perceived by the Jewish people as one of the enemies in the history of the Jewish people."

A compromise was struck within David's family. Everyone would draw breath, and wait. David's will did not waver. At the age of 26, he was baptised.

But he insists that through that period, and since, he has integrated what he calls "my two identities".

"I feel very strongly historically, socially, ethnically - in all senses other than religiously - a Jew. And then, integrating with that, who I am as a person in relationship with God. And it's not easy. There are no simple solutions."

Some of the community to whom Father Neuhaus ministers, as one of the five vicars of the Latin Patriarch of Jerusalem, are Catholics who are living for a short time in Israel, and who want to attend a Mass in the local language; some are expatriates who have married Israelis; and some, as with him, have converted from Judaism.

Did he, I asked him, still go to synagogue? A pause. "I do go, discreetly," Father Neuhaus replied. And then a laugh: "Now I'm saying it [in] public."

He often goes to the Friday night services in a reform synagogue which welcomes non-Jews.

"I'm not exactly a non-Jew," he says. "In a certain sense, I'm worse than a non-Jew. And yet I've been welcomed for who I am, and with a sensitivity to this tension."

Not often will you hear a Catholic priest say that part of his identity is fulfilled through the synagogue service, or through participation, with friends and family, in Jewish feasts.

But Father Neuhuas is not unique. Grzegorz Pawlowski, a 78-year old Holocaust survivor from Poland, lives in a small and simply-furnished apartment in Jaffa.

In a level voice, but with his eyes still wide with the memory, Grzegorz related the long story that wound on from the moment, at the age of 11, he was separated from his mother and sisters - whom the Nazis then shot and dumped in a mass grave.

Grzegorz survived for three years by wandering the streets and the countryside, and hiding.

He ended up, after the war, in an orphanage run by the Red Cross.

"I'm afraid to speak that I was Jew," he told me, swapping for the moment from Polish-accented Hebrew to halting English.

"I'm afraid. Because Jew - you can kill him, yes?" And so Grzegor allowed himself to be baptised, before the orphans were to receive their first communion.

It was the start of a journey to Catholicism, which ended with him being ordained as a priest in 1958. But he kept his secret identity for another eight years.

"I felt uncomfortable that I was denying, to my mother and to my father, the fact that I'm Jewish. And so in 1966, I wrote an article in a Catholic Weekly, and there I told my whole story… how I got through the Holocaust, and how I became a priest."

Through that article, Father Pawlowski made contact with the one surviving member of his family - his brother, whom he thought was still living in Russia, where he had first escaped to.

Instead, his brother had made it to Haifa, in Israel. Grzegorz's conversion was a source of pain to his brother. "He never accepted it, never accepted it."

A long sigh followed. "He was a very religious Jew. We had very good relations. But he prayed that I come back to Judaism."

Much as Father Neuhaus explained, Father Pawlowski says that his identity, too, cannot be folded into neat boxes.

"I am a Catholic priest, and I also see myself as Jewish. I am connected to the Jewish nation. On Yom Kippur, I fast. At Passover, I eat matzah."

Sometimes, in synagogue, he says, he has to remember not to cross himself, and kneel; in church he has to make sure he is not wearing his kippa (skull-cap). Father Pawlowski delivers this last reminder to himself in a flat voice, before breaking into a loud, wheezy laugh.

And he has one final commitment to his Jewish roots.

"Close to where my mother and sisters were killed [in Poland], there's a Jewish cemetery, where there is a memorial to my mother and all those who were shot. And I will be buried there, next to my mother, in the Jewish cemetery."

FROM A FATHER TO A DOCTOR

After spending the late morning with Father Pawlowski, I stumbled across Dr Shakshuka, on the fringes of the flea market, in Jaffa.

I ordered the cheap, but laughably misnamed "business lunch".

Within moments of my choice, the waiter descended on my table with eight dishes.

There were four types of meat, the sort that appears to have been cooked for a day at a low, slow heat, then given a massage, then sent on holiday, and only when it has become at one with its surrounding ingredients and is so relaxed that it falls off the bone at the mere approach of your fork, is it then ready to be served.

All the dishes (bar the bed of couscous) went some way to explain why fat is such a good convection agent for flavour.

The good doctor's real name is Bino Gabso. His place has been serving shakshuka (a breakfast dish of eggs poached in a spicy tomato sauce) and utterly un-businesslike lunches for 17 years. Before him, his father also had an eatery in Jaffa. The family came to Israel in 1949, from Libya.

I was barely able to talk after lunch, even after a large, strong Arabic coffee, but I managed to croak the tired journalist's question: "Is there a secret?"

"No," Bino replied with fetching directness. "It is Libyan food. There is no secret. In Tripoli, people only have food. They have nothing else in their lives. They don't have music, anything. When they're at work, all they think about is food, and how they're going to make it when they finish work."

Many may take issue with Bino's reduction of Libyan life culture to a mess of lamb and beans. But one thing is certain. If you have business to conclude, do it before you order Dr Shakshuka's business lunch, not after.