St. Ambrose was born around 340. He was trained as a lawyer and highly educated, and he tried to bring Greek and Roman intellectual culture into harmony with Catholic teachings. 

Ambrose became governor of Milan, and used his intellectual gifts to defend Christian doctrine even before he was baptized. During that time, a bishop named Auxentius led the diocese of Milan. He was a forceful speaker, but he followed the heresy of Arius, which denied Christ’s divinity. 

Despite the decrees issued from the Council of Nicea the previous year, many people, including a majority of bishops, thought Arianism was a more sophisticated version of Christianity. Bishop Auxentius was notorious for forcing clergy to accept Arianism in their own parishes. 

When Auxentius died, Ambrose was not yet baptized, but he had already shown the Catholics in Milan how much he knew and embraced the faith. Even though he was a catechumen, they considered him the most logical choice to succeed the heretical bishop. Emperor Valentinian helped the Milanese Catholics force Ambrose to become the bishop. Eight days after his baptism, Ambrose was consecrated on Dec. 7, 374. 

As bishop, Ambrose gave his wealth to the poor and the Church, and taught Church traditions, using the wisdom of Greek theologians. He used pre-Christian philosophy and literature to help his parishioners understand the faith, attracting many followers, including a young professor who went on to become St. Augustine of Hippo. 

Ambrose celebrated the Mass every day, finding time to write and counsel his flock and anyone else who sought him out — public officials, pagans, and sinners. He famously denied communion to Emperor Theodosius, who had ordered a massacre of some 7,000 citizens. The emperor repented after Ambrose’s chastisement, doing penance and reconciling himself to the Church. 

St. Ambrose died in 397, after serving as bishop for 23 years. He was made a Holy Father of the Church at the Fifth Ecumenical Council, and his writings remain a source of authoritative teachings.