Ut queant laxis is the hymn that gave the musical notes their names. Each line of its melody begins one step higher than the last, and around the year 1030 the monk Guido of Arezzo used those first syllables to teach his singers the scale: ut, re, mi, fa, sol, la. A thousand years later we still sing his do re mi.
So that with loosened voices your servants may sing the wonders of your deeds, wash the guilt from our stained lips, O holy John.
The words ask St John the Baptist to free the singer's voice. In the Gospel his father is struck silent before John's birth, and speaks again only on the day he names his son. So this is a song that asks for the gift of song, and the concert opens with it, as a way of asking permission to sing.