Council of Ephesus — Mary declared Theotokos

The Council of Ephesus was called to resolve the Nestorian controversy. Nestorius, the Patriarch of Constantinople, argued that Mary should only be called Christotokos (Christ-bearer), implying a division between the human and divine persons of Jesus. The Council, led by St. Cyril of Alexandria, vehemently rejected this, affirming that Jesus is one divine Person with two natures. Therefore, it is entirely correct to call Mary Theotokos (God-bearer or Mother of God), not because she originated God, but because the Person she carried in her womb and gave birth to was God the Son.