It all began when my father's youngest sister Steffi died in Jerusalem. Extraordinarily, the chevra kadisha responsible for her burial found a resting place for her on the Mount of Olives right next to her elder sister Eva, who had died some 65 years earlier, in 1943. My father would sometimes speak about Eva, how she became ill in impoverished wartime Palestine, how the doctor said she needed red wine and meat, how she died anyway. He called out for her often during his own final illness. But now I stood for the first time by her grave and read beneath her name a further inscription, one I had not anticipated seeing there and one that must have been organised by the family soon after the war, before East Jerusalem became Jordanian territory. It was in memory of Eva's grandmother, my great-grandmother, Regina Freimann, who perished in Auschwitz.

Soon afterwards, I was going through the contents of the flat in Rechavia where the family had lived for almost the whole time after they fled to Palestine in 1937. They were all gone now and I was helping my cousin with the sad task of clearing out two generations of belongings. In a case inside an old trunk lay a small, off-white linen bag. I opened it and withdrew a bundle of documents. They were mostly handwritten, in German, on frail airmail paper. There were bills, lists and letters; the earliest were dated 1938, the last 1947. I began to read: "…Ernst too has been arrested… After that, we heard no more… I am most anxious for our dear children."

I have been translating and thinking about those letters ever since. The names were not unfamiliar; my father had mentioned them to me - Sophie, Trude, little Arnold: "Sophie visited us in Palestine; we told her not to go back." "My husband's a Czech nationalist", she'd replied, "they won't let the Nazis through". My father had also asked me to prepare a list of the Hebrew names of the relatives who perished, which we placed next to the memorial lamp each Tisha b'Av. But he didn't dwell on these painful matters and I, like so many others, failed to ask when those who could have answered my questions were still alive.

I feel mindful now of the talmudic dictum about bringing speech to the lips of the dead. Sadly, there may soon be few survivors left and the closest to the sound of their own voices will be words like these, in handwriting hard to decipher on fading pieces of thin paper. I intend to explore as much as I can and then publish this testament to family love, to the manner in which they encountered their fate, to the destiny of our people.

My father's mother was one of six children. Their father, Rabbi Dr Yakob Freimann, head of the Orthodox rabbinical court in Berlin, died suddenly in 1937. His wife Regina later wrote that she was glad he was spared the terrible years that followed, and that she prayed daily that his spirit would hover over the family to guide and protect them. Three of their children, including my grandmother Ella, found refuge in Palestine. She had been living in Breslau when her husband, my grandfather, who owned a timber mill, was tipped off that he was high on the Gestapo list. They set the table for tea as if they were going on a brief excursion and left the city that evening, never to return. My father was 16. I once asked him if he had any good memories of Germany. "No," he replied; the Nazis had dominated it all.

I began to read… ‘Ernst too has been arrested…after that we heard no more… I am most anxious for our dear children’

My grandmother's sister Wally and brother Alfred also sought safety in Palestine. Alfred had been a judge. Forbidden even to enter the courtroom over which he had until recently presided, he determined to leave Germany at once. He went to Italy but, when his wife saw Mussolini's fascists, she insisted they move on to Jerusalem.

Alfred was burnt to death there in 1948 in the notorious attack on the convoy of scholars heading for the Mount Scopus campus of the Hebrew University. My father, who loved England, never forgave the British for standing by and doing nothing. Another sibling, Ernst, was imprisoned for several weeks in Sachsenhausen after Kristallnacht, but finally managed to obtain transit visas to Britain for himself and his family. Immediately prior to the outbreak of war, he sought permission to practise his profession of medicine.

He was informed by the Central Office for Refugees that, "the Home Office authorities have given us to understand that in the event of a national emergency the foreign doctors living in this country… may be allowed special concessions". His application was duly sent to the British Medical Association but, in the event, he travelled on to America.

My grandmother's remaining sisters, Sophie and Trude, perished along with their families. So did their mother, Regina. Among the documents I would later find were their final letters.

Matters didn't begin that badly. Sophie, who was beautiful, elegant and wealthy, wrote on July 11 1938 from Holleschau (now in the Czech Republic) to her mother in Berlin: "It's a bad year here for preserving fruit… On the other hand, I've put away ten kilos of blackcurrant compote and five of blueberries. I've still got so much jam from last year that I'm going to leave it until the raspberries before starting again."

It's strange how much such a small detail has affected me. I keep seeing my father teaching me how to bottle fruit in those large glass preserving jars which, until a couple of years ago, were thought to have gone out of fashion forever.

Just a month earlier, Trude had written from Posen, where her husband was a doctor in the Jewish hospital, complaining she hadn't received the customary greetings for her birthday. Nevertheless, she had celebrated in style with a least half-a-dozen different kinds of cake, real coffee and cream. I abandoned the dictionary; only an old cookbook and floury hands would tell me what Blechkuchen and Muerbekuchen had tasted like and even then, of course, they would never come out anything like as good. No doubt they were extremely rich: "Of course we were unhealthy when the recipes began 'One takes 20 eggs'," I remember my father once saying.

I have only two other letters from Trude, both sent from the ghetto town of Ostrow-Lubelski in the Lublin region, an area initially designated by the Nazis as a kind of Jewish reservation, prior to the decision that extermination was simpler. On October 31 1941, she wrote: "It's my best time of day when I go to bed (that is, the sofa) and read. Sadly the light doesn't always work all that well; we have electricity only in two rooms and as the current is provided by a mill there isn't always light and when there is, it flickers a lot.

"We also have two petroleum lamps but we don't light them very often as petrol has become very expensive. Everyone struggles on as best they can. Most people live off the sale of old stuff which gets sent to them."

Matters were clearly going to get far worse, but this was the last any of the family heard from her. After the war, her brother Ernst wrote to the president of the city of Poznan, asking if they could tell him anything of the fate of their former residents.

A certain M. A. Dropinski informed him that they had been taken from Ostrow-Lubelski to the nearby town of Lubartov on October 9 1943, and from there to Treblinka. He requested an administrative fee of 200 zlotys for the provision of this information.

Meanwhile, my great-grandmother, stuck alone in Berlin, was hoping to join her three children in Jerusalem. A letter was sent to her on November 9 1938 - the very morning before what was to become known as Kristallnacht, the Night of the Broken Glass - by the Palaestina Treuhand-Stelle, which represented Jews trying to obtain permits to enter Palestine: "Owing to the limited number of certificates made available by the Mandate Government, it will, according to current schedules, not be possible for the foreseeable future to obtain a pensioner's certificate to emigrate to Palestine."

This letter was effectively a death sentence. She might yet have managed to escape since, because of the diligent efforts of her son Alfred in Jerusalem, the requisite papers did finally arrive the following year. But in the meantime she had made the fatal decision to join her eldest daughter Sophie in Holleschau. No doubt the family thought that anywhere must be safer than Berlin, and that their elderly and recently widowed Mama must not be left to struggle on alone in such terrible times.

But after the Nazi annexation of the Sudetenland in October 1938, escape from Czechoslovakia became effectively impossible, whereas, had she remained in Berlin, she might just possibly have been able to get away - until Pearl Harbour and the entry of America into the war cut off that route as well.

I feel as if I have got to know my great-grandmother through the many letters she sent to her family in America. She addressed her post west rather than east because the only way of writing to Palestine, which remained in British hands, was via the Red Cross, where cards were strictly limited to 25 words.

She never once refers to a relative without preceding the name with the abbreviation "l" for liebe - dear. She almost never writes about herself but is always solicitous about others, their fortunes, their employment and their spirits. "Don't mourn the past but work for the future," she advises them.

She had a profound, immovable personal faith. Observing that a particular relative was of a nervous disposition and had made all his family anxious, too, she wrote in November 1941: "I maintain the view that just as our dear God has ordained them so shall things come to pass for the good, befall us whatever fate has been decreed."

Her last missive, a card sent from Theresienstadt, is postmarked February 25 1944 and stamped with the Nazi eagle. Last time I was with a group in Auschwitz-Birkenau, the frogs in the pond next to the ruins of Crematorium Three sang so loudly that our memorial prayer could scarcely be heard. My great-grandmother, whose ashes may have been in that very water, would have considered that those frogs, too, were part of God's creation and were, in spite of everything, continuing life's song of praise.

After the war, my grandmother Ella must have learnt that a distant relative, Charlotte Tuch, Trude's husband's sister, had survived underground in Berlin. Charlotte replied to her enquiry in January 1947, apologising for her delay: "As a result of everything we've been through, my husband and I have been in such a wretched state, both physically and mentally, that we are only gradually able to answer the many letters from abroad. The last letter I received from Alexander, Trude and Arnold was in August 1941.

"Your dear mother and Sophie still received a letter in October 1941, then they too heard no more… Your dear mother wrote the following words: In spite of everything, my faith in God remains unshakeable. These words accompanied me through the long years of persecution and bombing, when more than once our life hung by a silken thread, and gave me the strength to bear it all and to come through. We lived illegally for more than two years, that is, without reporting to the police and without ration cards and in constant fear of the Gestapo. But we retained the hope that when it was all over we would find our families. Only now, when everyone who has returned from the camps has been registered with the Jewish community in Berlin, have we finally buried our hopes…"

This bundle of letters is all that now remains to speak of my great-grandmother's last years and of Sophie and Trude, who were killed with their families. I read them not only as testaments to murder, but also to the deep bonds of family and to the undying importance of faith, nurture, and love and to the essential place in our lives of such ordinary matters as recipes and gardens. That is their victory.

Jonathan Wittenberg is senior rabbi of the Assembly of Masorti Synagogues UK