Legend states the St. Gregory The nice (d. 604) listened to the initial a few strains chanted by angels on a particular Easter morning in Rome when he walked barefoot in an awesome spiritual procession and that the saint thereupon extra the fourth line: “Ora pro nobis Deum. Alleluia.” Almighty, https://jeffreyzuiul.blazingblog.com/31240686/the-greatest-guide-to-vita-pro-nobis