While exploring Otto Klemper: His Life and Times you are quickly drawn into issues of self and family identity. From Page 7:

“In Breslau, where as in most of the cities of Eastern Europe, the Jewish community was still largely intact, the Klemperers' family life was later described by their younger daughter, Marianne, as ‘old-fashioned Jewish’: the Sabbath, feast days and dietary laws were all observed. In Hamburg, however, Nathan found employment in a Christian firm, which involved working on the Sabbath. From this time much religious observance was allowed to lapse. Though Nathan remained a member of a synagogue and observed fasts tot he end of his life, Ida, who had grown up in the less hermetic Jewish world of Hamburg, was deeply imbued with the ideal of assimilation. Yom Kippur was observed by the male members of the family, but dietary restrictions were gradually abandoned and Ida took her young children to a reformed synagogue, where the services were partly in German. On his thirteenth birthday, Otto was formally received into the Jewish faith at the ceremony of the bar mitzvah, but among the books he received as presents on that occasion were the complete works of Shakespeare. There was great emphasis on prayer, but the prayers were German. Grace was said at table in German. Traditional Hebrew songs gave way to German music. There was no mention of Zionism. Nor did Ida send her children to exclusively Jewish schools. Unlike his father, who had been raised in a closed Jewish society in Prague, Otto Klemperer was brought up as a German citizen of Jewish faith, a half-way house that was to fail to withstand the storms of the twentieth century.”