During the past several months of reading about different saints of the church, I've learned that a few of them have been formally declared Doctors of the Church, those who contributed specially to theology and doctrine. Cyril of Jerusalem (c. 313-386), whose feast day is today, was declared such a doctor by Pope Leo XIII in 1883. A bishop of Jerusalem, he is honored on Roman Catholic, Anglican, and Eastern Orthodox calendars today.
The Roman Catholic Saints site has this about him:
"The crises that the Church faces today may seem minor when compared with the threat posed by the Arian heresy, which denied the divinity of Christ and almost overcame Christinity in the fourth century. Cyril was to be caught up in the controversy, accused (later) of Arianism by St. Jerome (September 30), and ultimately vindicated both by the men of his own time and by being declared a Doctor of the Church in 1822.
"Raised in Jerusalem, well-educated, especially in the Scriptures, he was ordained a priest by the bishop of Jerusalem and given the task of catechizing during Lent those preparing for Baptism and during the Easter season the newly baptized. His Catecheses remain valuable as examples of the ritual and theology of the Church in the mid-fourth century.
There are conflicting reports about the circumstances of his becoming bishop of Jerusalem. It is certain that he was validly consecrated by bishops of the province. Since one of them was an Arian, Acacius, it may have been expected that his 'cooperation' would follow. Conflict soon rose between Cyril and Acacius, bishop of the rival nearby see of Caesarea. Cyril was summoned to a council, accused of insubordination and of selling Church property to relieve the poor. Probably, however, a theological difference was also involved. He was condemned, driven from Jerusalem, and later vindicated, not without some association and help of Semi-Arians. Half his episcopate was spent in exile … He finally returned to find Jerusalem torn with heresy, schism and strife, and wracked with crime. Even St. Gregory of Nyssa, sent to help, left in despair.
"They both went to the (second ecumenical) Council of Constantinople, where the amended form of the Nicene Creed was promulgated in 381. Cyril accepted the word consubstantial (that is, of Christ and the Father). Some said it was an act of repentance, but the bishops of the Council praised him as a champion of orthodoxy against the Arians. ..."