What significant event in church history was affirmed at the Council of Ephesus?

The Council of Ephesus, held in 431 AD, is most notably recognized for affirming the significant theological position regarding Mary's title as Theotokos, or "Mother of God." This title emphasizes the belief in the divine nature of Jesus Christ, asserting that because Mary bore Jesus who is both fully divine and fully human, she rightfully holds the title of the Mother of God. The Council addressed controversies surrounding this designation, particularly opposition from Nestorius, who argued for a distinction between the natures of Christ that ultimately undermined the notion of Mary as the Mother of God.

The event's significance lies in its impact on Christological debates and the affirmation of the unity of Christ’s two natures. By declaring Mary Theotokos, the Council sought to protect the doctrine of the Incarnation and to affirm the full divinity of Christ, which is critical to Christian theology. Thus, this affirmation at the Council of Ephesus shaped subsequent church teachings and has remained a key aspect of Marian dogma within Christianity.