The Council of Ephesus (431) upheld Theotokos for the Virgin Mary and defended the unity of Christ’s person, countering doctrines associated with Nestorius. Reaffirming the Nicene faith, the bishops received key letters of Cyril of Alexandria, condemned innovations to the creed, and issued canons guiding church order. Its decisions still shape Orthodox worship and doctrine.
The Council of Constantinople (381) reaffirmed the Nicene faith and expanded the creed to confess the Holy Spirit as “the Lord, the Giver of Life.” Confronting Apollinarianism and the Pneumatomachians, the bishops clarified Trinitarian doctrine and issued canons on church order. The resulting creed anchors Orthodox worship to this day.
The Council of Chalcedon (451) defined Christ as one Person in two natures—“without confusion, change, division, or separation.” Receiving the Tome of Leo and the earlier creeds, it clarified how the Church speaks of the incarnate Lord in worship and preaching and issued canons that influenced ecclesial order for centuries.
The Council of Nicaea (325) answered the Arian crisis by confessing the Son as “consubstantial” with the Father and issuing canons that shaped church life. Convened by Emperor Constantine, Nicaea provided the foundation of Nicene faith, clarified doctrine for worship and baptism, and set patterns of unity that endure in Orthodoxy.