Which doctrine did the Council of Ephesus affirm concerning Mary?

The Council of Ephesus, held in 431 AD, was pivotal in affirming the theological significance of Mary, emphasizing her title as Theotokos, which translates to "God-bearer." This title asserts that Mary gave birth to Jesus Christ, who is both fully divine and fully human. By declaring Mary as Theotokos, the Council clarified her role in the incarnation of Christ and countered various heretical views that denied the true divinity of Jesus.

This affirmation was crucial for understanding Christology—the study of the nature and work of Christ—by establishing that since Jesus is God, and Mary bore Jesus, she indeed has a special role in salvation history as the one who bore God in human form. This decision helped shape Marian doctrine in Christianity, leading to deeper reverence for Mary within the Church. The recognition of Mary as Theotokos eventually influenced various liturgical practices and dogmas concerning her role in salvation.