Whether or not he was the greatest musician of his generation is subject to debate. Leonard Bernstein himself certainly thought he was. Was he one of the greatest Jewish musicians of the 20th century? No doubt whatsoever. In an age that produced an Artur Rubinstein, an Isaac Stern, to say nothing of an Itzhak Perlman and a Daniel Barenboim, Leonard Bernstein was uncompromising in two things - his music and his Jewishness.

With the possible exception of Perlman, who loves Jewish music, no other figure who stood on the podium or sat at the piano keyboard or at his desk writing some of the most memorable music of his time, let the world know he was not just a musician and a Jew but a Zionist from his toes to every one of his silvery hairs.

It came out in his broadcast lectures, which were both educational and wonderfully entertaining. Whether it was conducting the Israel Philharmonic or entertaining troops in the Six-Day War, there was always, metaphorically, a blue and white flag fluttering behind him. When he wrote his Kaddish symphony it was easy to imagine him standing in shul.

Other pianist-musicians I have known, like the brilliant Andre Previn, with whom I spent a good deal of time writing his biography, have allowed their Jewishness to slide. "It is not a code I follow," he told me once - and then recalled how he had once slapped the older conductor on the back, saying: "Hi, Jewboy! Lenny wasn't offended, but clearly if a non-Jew had said it, he surely would have been.

Bernstein's death 25 years ago this month was mourned not just by classical music lovers, but also by people who really didn't know much about music, but whistled and hummed Tonight and every other tune they could remember from West Side Story or one of his other musical shows like Wonderful Town.

Secretly, I always thought of Bernstein as the second coming of George Gershwin, but he was more than the second anything. Anyone who could produce both New York, New York (not the Sinatra hit, but the big number from On The Town, which became the first Hollywood musical shot on location) and the Chichester Psalms, with its original Hebrew sung by a choir, was plainly exceptional.

I have a personal reason to think affectionately of this towering figure in Jewish life. He liked my book which I wrote in the 1980s, even to the extent of allowing a photographer from the Mail on Sunday magazine to snap him reading it. But it was not an easy journey. I interviewed him for the Today programme on Radio 4 and we, shall we say, didn't exactly hit it off at that first meeting. "Mr Bernsteen," I began (the reason I now spell it that way will become immediately apparent.) "Bernsteen!" he positively thundered. "Bernsteen! It's Bernstyne! Mr Freedland, Bernstyne!" It was to get worse. "You are something of a showman, Mr Bernstein aren't you?" I dared to ask. "A showman! A showman!" I might just as easily have called him a serial murderer at that moment. "I'm a musician, Mr Freedland. A musician."

Could I ever have doubted that? But this was the conductor who seemed to dance when he had a baton in his hand. He would jump and he would almost fall to his knees. And when he finished, he wouldn't just invite the audience to clap his orchestra members, he would go to each player and kiss them. I can remember the Proms concert at the Albert Hall when he conducted Mahler's Fourth Symphony - Mahler was not only his favourite composer but he was regarded by many as the foremost exponent of his work. He was getting quite old and suffered from emphysema. There was a female singer for the performance who not only sounded as beautiful as a bird on an early spring morning, she looked ravishing. Study the people in the hall and you saw that all eyes were on her. For the first few minutes, that is. Then, watch that audience again and see that those eyes had switched to the now rather fat, coughing Bernstein. Wonderful music sounding even more wonderful through his magic touch, yes, but I am not sure that it wasn't also showmanship.

Is there any doubt why I took to him? The fact that he was so proud to be Jewish might have had something to do with it, too.

Not surprisingly, his upbringing had been pretty influential. He talked about his parents, Sam and Jennie (originally Chaya) Bernstein, from Ukraine- and his aunt Clara - constantly in his famous TV lectures. He doesn't seem ever to have acknowledged that, when he was born in 1918 in the family home in Lawrence, Massachusetts, he was originally called Louis. Neither parent liked the name and changed it to Leonard, although forever after they, and seemingly everyone else, called him Lenny.

He wasn't to make much of the fact either that his father was in the beauty products business or that his parents stayed married simply because they thought it was the right and the Jewish thing to do. His brother Burton was to write in the New Yorker that Jennie was told by her mother: "When the rabbi speaks, step on Sam's foot and you will always be the boss." Jennie herself would say, "how wrong could my mother be!" Wrong or not, the one thing they agreed upon was the pride they had in their eldest son.

When Lenny made his unexpected debut at Carnegie Hall in 1943 - the conductor Bruno Walter having been taken ill - Bernstein, the understudy took over for an afternoon concert, which received plaudits from the stunned New York music critics that took him on his way to the top - the first call he made was to his parents in Lawrence.

Sam's one-word retort was in Yiddish: "Gevalt!"

When Lenny married his wife, the Costa Rica-born Catholic actress Felicia Cohn Montealegre, she agreed to convert to Judaism, informing the Orthodox rabbi who performed the ceremony under the chupah that her great grandfather had been a rabbi, a Reform rabbi.

It didn't stop Sam complaining that she was a "shiksa". But the Bernsteins eventually took to her and to the three grandchildren - two girls and a boy - whom the couple gave them.

Plainly, Lenny thought as a Jew - and one who had a profound knowledge of Judaism and Jewish culture.

If there was another religion in his life it was probably a deity called Serge Koussevitzky, who was born Jewish but drifted away. The Russian-born conductor was his idol.

He had a ritual that Bernstein adopted and carried out before each concert - first, the shower and then the donning of a crisp, new, white shirt and a newly pressed tailcoat.

The always immaculately dressed Lenny usually maintained he was not superstitious. The routine, he said, felt to him like the ablutions of the High Priest before entering the Holy of Holies in the Temple on Yom Kippur.

For him, his music itself was practically holy and this was a way of demonstrating it - while giving it in his mind a totally Jewish flavour.

Israel was more than just a flavour. It was part of the plasma in his blood that began to stir with the establishment of the State in 1948.

The birth of Israel meant the rebirth of the Palestine Symphony Orchestra, now as the Israel Philharmonic. To him, the men and women playing in that orchestra were as much fighters for the infant state as those other civilians - many of whom, like them, were Holocaust survivors - who were grabbing what arms they could to defend their country. They fought, he believed, with pianos and violins and French horns.

He went to conduct the orchestra on its home turf whenever he could, and often on tour in America. Impresarios in the Jewish state only had to hear his name to get on the phone to New York and try to set up a Bernstein season - not easy since he was always booked years in advance. He regularly performed at concerts in aid of charities like the Hadassah Hospital and, above all, for the Israeli troops. For some reason, the soldiers always demanded Mozart, although he never worked out why.

Music was always there, ready to solve problems, big and small. There is a strong case to suggest that a crucial battle in the War of Independence was partly won by Leonard Bernstein . He was on the podium at a makeshift army base in the Negev, playing his Mozart symphony and an encore of Rhapsody in Blue. Word had got out that this was a magnificent concert. One platoon informed another and in a matter of minutes, a column of jeeps and makeshift trucks were processing towards the do-it-yourself concert hall.

The parade was not to go unnoticed by the enemy. An Egyptian spotter plane radio-ed to base that an enormous company of Israelis were about to attack their troops near the then isolated desert village of Beersheva. Orders were immediately given to retreat.

That, of course, was what he never did - retreat.