Legend suggests the St. Gregory The nice (d. 604) listened to the very first three strains chanted by angels on a specific Easter early morning in Rome whilst he walked barefoot in a fantastic religious procession and that the saint thereupon included the fourth line: “Ora pro nobis Deum. Alleluia.” https://sergiojrwgk.blog-eye.com/31270140/the-greatest-guide-to-vita-pro-nobis