Today was, after being instituted by Pope Pius XI in 1931, the Feast of the Divine Maternity of Our Lady. It was established in honor of the anniversary of the great Council of Ephesus in 431AD, at which Our Lady was defined as Theotokos -- Mother of God -- and the Nestorian heresy was condemned.
Theotokos of Vladimir.
In 428 Nestorius, originally a monk from
Antioch, was made Patriarch of Constantinople (428-431). This eloquent and austere new Patriarch, his
first Christmas as shepherd of the Imperial capital preached that Mary was not
the Mother of God! Behold, the Nestorian
heresy. He, and the Nestorian heretics, claims that Christ is not actually God,
but God only dwells in him as “in a temple” or “a garment.” Thus, there are two persons in Christ – and Mary was only mother of
the human person, not the divine. Thus,
she is not Mother of God, but only Mother of Christ! This caused quite the stir in the area, as
you might imagine. A lawyer actually
interrupted his homily in the Cathedral, and he would be faced by another
bishop on the next feast of the Annunciation.
Copies of these
homilies reached the Patriarch of
Alexandria, St. Cyril (Successor of St. Mark from 412-444AD), in 429 and he immediately condemned the
ideas and reported them to the pope, St.
Celestine I (Successor of St. Peter from 423-432). Nestorius,
for his part, appealed to the Eastern Roman Emperor, Theodosius II (Reigned, 408-450).
The Pope, agreeing with St. Cyril, condemned the teaching of Nestorius,
and threatened to depose him. He, for
his part, persisted, and this with the encouragement of Patriarch John of
Antioch (Successor of St. Peter from 428-442).
Ephesus today: the Library of Celsus.
The Emperor, Theodosius II, hoping to find a solution,
summoned a general council – the Third – at Ephesus which met in 431. St. Augustine was actually invited, but he
had died by the time the invitation arrived.
After a delay, owing to the absence of John of Antioch, the council
finally opened in the blazing heat of June 431, with Cyril of Alexandria
presiding as legate of the Pope. The
Council carefully read the teachings of Nestorius, and quickly condemned them. Nestorius himself was given three warnings to
arrive and answer, but he refused, and was deposed. The Council unanimously declared that Mary
was, indeed, Theotokos! Torch-lit processions and celebrations met
the declaration in Ephesus.
A more thorough account of the Council can be found here: Old Catholic Encyclopedia: Council of Ephesus
St. Mary, Mother of God, pray for us sinners, now and at the hour of our death!