On January 18, the Holy Church commemorates Saint Cyril, Archbishop of Alexandria along with Saint Athanasios the Great.
The reason behind the celebration of the holy memory of Saint Cyril on January 18 is his journey from Alexandria to Ephesus for the convention of the Third Ecumenical Council.
(June 9th is the day of the commemoration of Saint Cyril)
In 431, the Council of Ephesus was called just 50 years after the Council of Constantinople (Second Ecumenical Council).
Nestorius, the reason behind the calling of the council did not choose to attend the council. By 431, he was 50 years old. He was educated in Antioch and was a monk well known for his great preaching ability. Because of his great skills as an orator, he was chosen to be bishop of Constantinople in 428.
The Nestorian heresy essentially claimed that Jesus Christ is two-separate-persons and therefore, we can’t call Mary the Theotokos (God-Bearer), but calls her Christotokos (Christ Bearer – bearer of the human person). There are two points we need to point out here. First, when you say something wrong about Mary, you usually say something wrong about Christ. Second, Nestorius denies the Incarnation and claims that Christ’s human flesh was an indwelling. He denied the true humanity of Jesus Christ.
At the Council of Ephesus in 431 A.D., the Council Fathers declared that Mary is Theotokos – God Bearer. Mary bore in her womb the Son of God making her the Mother of God. Nestorius was excommunicated and he was unseated from his position as Patriarch of Constantinople. Nestorius was branded as “the new Judas.” As the bishops returned to their lodging after the formal declaration, the lay faithful of Ephesus gathered and passionately supported the bishop’s decision to excommunicate Nestorius and to show their love for the Blessed Mother by shouting, “Hagia Maria Theotokos” and “Praised be the Theotokos.”