O Magnum Mysterium is a responsorial chant from the Matins of Christmas Day. This version by Morten Lauridsen is so, so beautiful. Take a moment and let it touch your soul.
O great mystery
and wondrous sacrament,
that animals should see the newborn Lord
lying in their manger.
Blessed is the Virgin whose womb was worthy
to bear the Lord Jesus Christ. Alleluia!