Creed promulgated
The Creed of this Council
We do not say that the nature of the Word was changed and became flesh, or that it was converted into a whole man. But rather that the Word, having personally united to himself flesh animated by a rational soul, did in an ineffable and inconceivable manner become man. There is of both one Christ and one Son. We do not mean that the difference of the natures is taken away by the union; but rather that the divinity and humanity, through their mysterious union, make perfect the one Lord Jesus Christ.
Definition · No. 1
The Council's Answer
Claim refuted: "“Mary bore a human being, Jesus, who was the dwelling-place and instrument of the divine Logos. The two are united in a voluntary moral union. Properly speaking, God did not suffer and die; the man Jesus did.”" — If the two natures are only morally united, there is no genuine Incarnation. The subject of Christ's sufferings is a human being, not God. The gap between Creator and creature remains unbridged. There is no genuine communication of divine life to human nature in Christ, and therefore no basis for the deification of human persons united to him.
Creed · No. 2
St. Cyril's Second Letter to Nestorius, ratified by the Council
We do not say that the nature of the Word was changed and became flesh, or that it was converted into a whole man. But rather that the Word, having personally united to himself flesh animated by a rational soul, did in an ineffable and inconceivable manner become man. There is of both one Christ and one Son. We do not mean that the difference of the natures is taken away by the union; but rather that the divinity and humanity, through their mysterious union, make perfect the one Lord Jesus Christ. — St. Cyril of Alexandria, Second Letter to Nestorius — read and approved by the Council of Ephesus, 431 AD
Anathema · No. 3
Against Nestorianism
“Mary bore a human being, Jesus, who was the dwelling-place and instrument of the divine Logos. The two are united in a voluntary moral union. Properly speaking, God did not suffer and die; the man Jesus did.”
Definition · No. 4
Witness — St. Cyril of Alexandria (Champion of Orthodoxy)
"The holy Virgin bore in the flesh God who was united with flesh by hypostasis. For this reason we call her Theotokos — not that the nature of the Word or his Godhead received its beginning from the holy Virgin, but since of her was born that holy body with a rational soul, to which the Word was hypostatically united, he is said to be born according to the flesh." — St. Cyril, Third Letter to Nestorius, 430 AD. The precision here is critical: the Theotokos title does not claim that Mary is the origin of the divine nature, which would be absurd. It claims that the Person she bore — the hypostasis, the subject — is the eternal Son of God. The flesh is his, the Person is eternal.
Definition · No. 5
Witness — Nestorius of Constantinople (The Condemned)
"Tell me, does God have a mother? In that case we excuse paganism, which talks of mothers of the gods. Paul, however, says of the Son of God that he was “made of the seed of David according to the flesh” and “born of a woman” — not God born of a woman. He who was formed in the womb is not God himself, but God assumed him. He did not make the one assumed into God from the beginning, but through the progress of his actions he showed him worthy of God." — Nestorius, First Sermon against Theotokos, 428 AD. The problem Cyril diagnosed: Nestorius's language implies two subjects — “God assumed him.” If there is an “him” to be assumed, that “him” is a person distinct from the divine Logos. The council found this incompatible with “the Word became flesh.”
Definition · No. 6
Witness — The Congregation Outside the Doors (The People of Ephesus)
"When the definition was read, there arose a great cry in the city of Ephesus, the people praising and extolling the assembly for their upright judgment. For the whole city — from the first hour of the night until dawn — was illuminated with torches. Women greeted the bishops with incense as they left. All the people praised the definition with one voice." — Acts of the Council of Ephesus, Account of the First Session, 431 AD. The reception of the council by the faithful of Ephesus — who venerated Mary as Theotokos from ancient times, in the very city where she was believed to have lived after the Crucifixion — exemplifies the Orthodox understanding of conciliar reception: the council speaks for the Church, and the Church's recognition of that voice confirms its authority.