What aspect of St. Ambrose's leadership is he notably recognized for?

St. Ambrose, the Bishop of Milan in the late 4th century, is particularly recognized for his courageous stance in excommunicating the emperor Theodosius I due to moral reasons following a massacre in Thessalonica. This act exemplifies his commitment to the principles of justice and the moral authority of the Church over secular power. His willingness to confront a powerful leader for the sake of upholding Christian ethics made a significant impact, illustrating the Church's role as a moral compass in society. This event not only reinforced the Church's independence from state influence but also established Ambrose as a formidable figure in ecclesiastical history, showcasing the balance he sought between piety and civic accountability. His actions set a precedent for later Church leaders regarding the relationship between the ecclesiastical and political realms.