« IAM LUCIOS ORTO SIDERE ». – Hymn sung at the beginning of the hour of Prime, composed by an unknown author of the school of St Ambrose, hence called Ambrosian. Indeed, St Benedict in his Rule says: « indessequitur ambrosianum » (ch. 12).
At the dawn of the new day, when the darkness of night has been dispelled, the prayer of the faithful rises to God, seeking His aid for the fulfillment of the day’s duties and for avoiding those defects which bring such grave harm to the life of the spirit. For the grace of the Lord is indeed the salvation of man; through it good works are accomplished, and by it thoughts and deeds are directed toward God.
Bibl.: G. B. Belli, Gli inni del Breviario tradotti, Roma 1856, pp. 125-126; S. Baumer, Histoire du Breviario romain, I, P. 1869, pp. 167-168; F. Vandersuyf, Les hymnes de l'Ordinairé du Breviario romain, iv 1922, pp. 36-37; A. Mirra, Gli inni del Breviario romanzo, Napoli 1947, pp. 45-46.