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 whilst he walked barefoot in an incredible religious procession and the saint thereupon added the fourth line: “Ora pro nobis Deum. Alleluia.” Almighty, https://nervocure58000.bcbloggers.com/30555627/facts-about-vita-pro-nobis-revealed