A piece for organ and voice on the model of the medieval missa alternatim, in which a liturgical text and its corresponding Gregorian melody are delivered alternatively on the organ and vocally, each instrument featuring a different kind of ornamentation on the basic chant. This piece uses the liturgy for the feast of St. John the Damascene because the premiere happened to be scheduled on that day. Commissioned by the Orgelpark and premiered at the Orgelpark in Amsterdam (Netherlands) in December 2007. Performed again at the Nederlands Gregoriaans Festival in Ravenstein (Netherlands) by Marcel Verheggen on June 14, 2014.