What theological concept was discussed at the Council of Ephesus?

The correct answer focuses on the discussions at the Council of Ephesus, which convened in 431 AD primarily to address significant theological controversies surrounding the nature of Christ and the role of Mary. The council is best known for condemning Nestorianism, a belief that separated the two natures of Christ, suggesting that there were two separate persons—one divine and one human—rather than one person with two natures. This understanding was seen as contrary to the orthodox view and posed a challenge to the recognition of Mary as the Theotokos, or "God-bearer," affirming her role as the mother of Jesus in his entirety, both divine and human.

The discussions on Marian doctrine were a crucial part of the debates, as the recognition of her title as Theotokos was essential for upholding the unity of Christ’s nature. Thus, the Council of Ephesus played a pivotal role in articulating and defending these theological concepts, which have had lasting implications in Christian doctrine.