Why did Cyril of Alexandria oppose Nestorius?

Cyril of Alexandria’s opposition to Nestorius was driven by both theological conviction and political rivalry between the episcopal sees of Alexandria and Constantinople.12

Theological Grounds

The primary theological conflict concerned the Incarnation and the unity of Christ’s person. Cyril emphasized the hypostatic union, insisting that the divine and human were inseparably united in one person. He championed the title Theotokos ("God-bearer") for the Virgin Mary to affirm that the one born of Mary was truly God incarnate.342

Cyril argued that Nestorius’s refusal to use this title, and his emphasis on the distinctness of Christ’s natures, effectively split Christ into two separate persons—one divine and one human—acting in concert. To Cyril, this undermined the reality of the Incarnation and the purity of the faith.3521

Political Context

Beyond doctrine, the conflict reflected broader power struggles. The see of Alexandria feared the growing influence of Constantinople. Cyril, acting as a powerful political and religious leader, sought to defend his authority and the orthodoxy of his tradition against the perceived errors of the Antiochene-influenced Nestorius.521