The origins of the Medieval Latin responsorial chant known as “O Magnum Mysterium” are not really clear any more. It’s early; before the tenth century. “O Magnum Mysterium” was part of the matins service for Christmas. For much of the Middle Ages, matins took place roughly at midnight. The Latin text describes the nativity scene in which Christ was born and laid in a manger, and animals were witnesses to the sacrament of his birth: O magnum mysterium, et admirabile sacramentum, ut animalia viderent Dominum natum, jacentem in praesepio! Beata Virgo, cujus viscera meruerunt portare Dominum Christum. Alleluia. In English: O great mystery, and wonderful sacrament, that animals should see the…