There is an interesting article on the fascinating history of the Kal Nidre prayer written in the Times of Israel by Rabbi Dr. Nathan Lopez Cardozo   http://blogs.timesofisrael.com/the-trouble-with-kal-nidrei/.  He asks why in the prayer, which reads like a legal statement we ask to annul vows and promises on the eve of the most solemn day of the Jewish year. Cardozo refers to the theory given in a book by Dr. Joseph S. Bloch that the famous prayer was instituted in the seventh century when the Visigoths forced Spanish Jews to convert to Christianity.  As Cardozo writes,

"Many of the Jews decided to save their lives by openly accepting Christianity while secretly trying to live a Jewish life. These were the first marranos or conversos. On Yom Kippur, however, they were struck by pangs of conscience. Secretly arranging synagogue services, they would begin by asking God for forgiveness on this solemn day, wanting to first rid themselves of their vows to Christianity. How could they stand before God while still under the vow of the Christian faith?"

Cardozo suggests that although we are "no longer forced to convert to Christianity, or any other religion," Jews today have "willfully adopt philosophies that estrange them from their Jewish roots "and have come to believe that Judaism is outdated. He suggests that "On Yom Kippur, even a Jew with only the slightest Jewish affiliation knows that he needs to undo his marrano status and annul his vows to radical secularism."

Relatively few Jews know of the apparent influence of the Kal Nidre prayer on Beethoven. I happened to come across some fascinating information online about how the main theme in the sixth movement of Beethoven's String Quartet Op. 131 appears to be based on the Yom Kippur Kal Nidre melody. In 1825, the Austrian Emperor allowed the Jews to build a great synagogue in Vienna in a residential complex where no one seeing the synagogue could identify it as such from the street. The synagogue, one which I visited , is known as the Stadttemple or Seitstettengasse Synagogue.  Interestingly enough, when this synagogue, was about to be dedicated, the Viennese Jewish community leaders sought to commission a work from Beethoven, asking him to write a cantata for the inauguration of the new synagogue.Alas, Beethovan eventually declined to do so.

 According to the Reform Judaism website, the main theme in the sixth movement of Beethoven's String Quartet Op. 131 [which was written shortly after Beethovan was approached to write a work for the synagogue in Vienna] "appears to be based on the Kol Nidre melody."

According to the site, when leaders of the Jewish community in Vienna approached Beethoven to compose music for the inauguration of a new synagogue, they were looking for music of a "Jewish character.

They " they supplied the composer with what they considered important examples of Jewish music, among them Kol Nidre. The commission was never completed, but since this is the only formal connection that can be established between Beethoven and the Jewish community, this brief contact is the likely source of the composer's inspiration."(http://www.reformjudaism.org/sounds-kol-nidre).

See also: http://thanbook.blogspot.ca/2009/02/beethovens-jewish-side.html