This illustrious light of Orthodoxy in the Western Church was born in Gaul in 349, but his widowed mother took the family to Rome while he was still a small child. Brilliant and well-educated, he was made a provincial Governor in 375 and took up residence in Milan. In those days, the Arian heresy was still dividing the Church, despite its repudiation at the Council of Nicaea in 325. When the time came to elect a new Bishop in Milan, the Orthodox and Arian parties were so divided that they could come to no agreement on a new Bishop. When Ambrose came as Governor to try to restore peace and order, a young child, divinely inspired, called out "Ambrose, Bishop!" To Ambrose's amazement, the people took up the cry, and Ambrose himself was elected, though he tried to refuse, protesting that he was only a catechumen (it was still common in those days to delay Holy Baptism for fear of polluting it by sin). He even attempted to flee, but his horse brought him back to the city. Resigning himself to God's will, he was baptized and, only a week later, elevated to Bishop. Immediately, he renounced all possessions, distributed all of his money to the poor and gave his estates to the Church. Straightaway, he entered into a spirited defense of Orthodoxy in his preaching and writings to the dismay of the Arians who had supported his election. Soon he persuaded Gratian, Emperor of the West, to call the Council of Aquilea, which brought an end to Arianism in the Western Church. (Arianism, however, continued to prosper among the barbarian nations for many years; see the Martyrs of Africa, also commemorated today).

Several times the holy Bishop was called upon to defend the Church against domination by the secular powers. Once, putting down an uprising in Thessalonika, the Emperor Theodosius punished the city by ordering the massacre of thousands of its residents. When the Emperor later visited Milan and came to the Cathedral to attend the Liturgy, Saint Ambrose stopped him at the door, condemned his crime before all the people, forbade him entrance to the church and excommunicated him for eight months. The Emperor went away weeping, and submitted in humility to the Church's discipline. When he returned after long penance to be restored to Communion, he went into the sanctuary along with the clergy, as had been the custom of the Emperors since Constantine the Great. But again the holy Ambrose humbled him in the sight of all the people, saying "Get out and take your place among the laity; the purple does not make priests, but only emperors." Theodosius left without protest, took his place among the penitents, and never again attempted to enter the sanctuary of a church. (When the Emperor died, it was Bishop Ambrose who preached his funeral eulogy).

Saint Ambrose, by teaching, preaching and writing, brought countless pagans to the Faith. His most famous convert was St Augustine (June 15), who became his disciple and eventually a bishop. Ambrose's many theological and catechetical works helped greatly to spread the teaching of the Greek fathers in the Latin world. He wrote many glorious antiphonal hymns which were once some of the gems of the Latin services.

Saint Ambrose reposed in peace in 397; his relics still rest in the basilica in Milan.