Schönberg wrote the biblical opera Moses und Aron between 1927 and 1932. He wrote it as a statement against anti semitism, but left it unfinished with the third and final act missing. It premiered in 1951, just 11 days before the composer’s death. Until then it was not performed because of the plans to finish it. That never happened. Composer Zoltán Kocsis wrote a third act in 2010, with permission of Schönberg’s heirs. Usually it is the last Schönberg version with the missing third act that is performed.
The original version in German is spelt Moses und Aron. The missing second a in the spelling of Moses priestly brother might be because of the composer’s incessant superstition: the title counts 13 letters.
The opera follows the events in the Book of Exodus of the Bible, where Moses is asked by God to lead his chosen people out of captivity in Egypt, across the desert to the Promised Land. A very Zionistic subject I suppose.