O MAGNUM MYSTERIUM is a brief but powerful piece that I wrote for a small church choir directed by my wife, Patrizia, for Christmas of 2010. It was meant as a gift for these good people that came once a week to prepare Christmas songs. The piece should have stayed in the drawer until the following Christmas. However, even during the first rehearsals I noted that the choristers showed a great enthusiasm in singing this composition of mine. Because of this, during the year that followed, I decided to show it to other well-known choirs. To my great surprise, the celebrated Vancouver Chamber Choir agreed to perform the world premiere of the piece in October 2011. A month later, another excellent Canadian ensemble, the Elektra Women's Choir, premiered the version for two equal voices, cello and organ, which I had prepared in the meantime. Many other performances followed in various parts of the world. I would like to mention a magnificent interpretation of my piece by the East Carolina University Chamber Singers, conducted by Andrew Crane and another one with Calicantus Children's Choir, conducted by Mario Fontana.