They reject the Third Oecumenical Council, and though showing the greatest devotion to the Blessed Virgin, deny her the title of Theotokos, i.e.
Cyril and his friends accordingly assembled in the church of the Theotokos on the 22nd of June, and summoned Nestorius before them to give an account of his doctrines.
The secret of the enthusiasm of the masses for the analogous expression Theotokos is to be sought not so much in the Nicene doctrine of the incarnation as in the recent growth in the popular mind of notions as to the dignity of the Virgin Mary, which were entirely unheard of (except in heretical circles) for nearly three centuries of the Christian era.
Hence the Nestorians, who insisted upon the duality of the natures to such a degree as to lose sight of the unity of the person, and who rejected the term Theotokos, repudiated the decrees both of Ephesus and of Chalcedon, and upon the promulgation of the decrees of Chalcedon formally separated from the church.
Peter and Paul, August 1-15 preceding the Feast of the Sleep of the Theotokos, and the six weeks before Christmas.