Legend suggests the St. Gregory the Great (d. 604) read the very first a few lines chanted by angels on a particular Easter morning in Rome even though he walked barefoot in a great spiritual procession and which the saint thereupon additional the fourth line: “Ora Professional nobis Deum. Alleluia.” https://vita-pro-nobis09864.blogadvize.com/38163577/new-step-by-step-map-for-vita-pro-nobis