Christology is the theology of Jesus – his nature, role, and person. In the earliest centuries of Christianity this meant taking Jesus from the Jewish Messiah (or messiah) and elevating him to the Son of God, and then to God made flesh. His death was transformed from a martyrdom to a deicide – the slaying of a god. At least that’s what the anti-Arianists determined at the first ecumenical council, the Council of Nicea in 325 CE. That’s when Trinitarian Patriarchs agreed upon the definition of a true professing Christian with the Nicene Creed. This Creed expresses a belief that the Christian God, Christ, and Holy Spirit are all part of the same uncreated, timeless Being.
After all the drama, bloodshed, and attempted excommunication of the Second Council of Ephesus, Pope Leo I wanted a chance to set things right, and on his own turf. He asked Emperor Theodosius II to convene another ecumenical council, but the ruler of the Roman/Byzantine empire wouldn’t. Instead he kept appointing bishops more supportive of Dioscorus than Leo. This was against the advice and wishes of Theo’s big sister and former regent guardian Pulcheria. When he had been just a boy of 7, Theodosius had named 15-year-old Pulcheria “Augusta”, freeing them from outside control. She’d had more power than any other woman in the Byzantine world ever since.
Pulcheria used that power to persecute Jews during her time as regent, passing laws to destroy all synagogues. In later years she believed that the Nestorian heresy had Jewish roots. Nestorianism was the belief Jesus received a human body from his birth through Mary, but divine Logos (the Word that was God and is God) existed separately. This separation was the repulsive heresy to those who came to be known as orthodox Christians. Heterodoxy and orthodoxy were still being determined: that was the point of ecumenical councils.
Arianists believed Jesus was a created being, God’s son, but not God. Ebionites were Jews who thought Jesus was their Messiah but nothing more, no divine spark in him, just a mortal man. Gnostics of Syria and Egypt couldn’t even agree amongst themselves – was Christ a supreme being, perhaps an angel. or a was he just a big con? The monophysites thought he had one divine nature, miaphysites thought it was two united natures, and duophysites thought it was two “consubstantial” natures. It was definitely time for another ecumenical council to figure out how much sugar and spice Jesus was made of.
In 450 CE Theodosius fell off his horse and died. The Roman Senate wouldn’t let Pulcheria rule on her own, even though she’d done at 15, so she married Marcian to co-rule. He agreed to let Pope Leo have his Council, but not where Leo asked to have it, in Italy. Contemplate the weak power of the Pope in 451. This was the third ecumenical council in a row he would not be able to attend, because it was not being held in Italy. Leo could not travel because Atilla the Hun was thinking about sacking Rome. Once again Leo sent a legate in his place, knowing the last time he had done that, the Coptic Pope had tried to excommunicate him.