Legend claims the St. Gregory the Great (d. 604) listened to the primary three traces chanted by angels on a specific Easter morning in Rome when he walked barefoot in a fantastic spiritual procession and the saint thereupon included the fourth line: “Ora pro nobis Deum. Alleluia.” Almighty, everlasting God, https://landenegvod.blogs100.com/31596277/considerations-to-know-about-vita-pro-nobis