“But, dear Beethoven, what have you done again?” Even if the authenticity of this statement, which was quoted by Anton Schindler, may be doubted, it reflects quite well the confusion that the Mass in C may have caused its commissioner, Prince Nicholas II Esterházy, in 1807. Unconventional for those times, here Beethoven opened up entirely new worlds of expression for the liturgical text, opening up new avenues for the further development of mass compositions in the 19th century.

This importan...