Legend suggests the St. Gregory the Great (d. 604) read the very first a few lines chanted by angels on a particular Easter early morning in Rome even though he walked barefoot in a great religious procession and the saint thereupon added the fourth line: “Ora pro nobis Deum. Alleluia.” https://vitapronobis78956.blogdeazar.com/31302867/rumored-buzz-on-vita-pro-nobis