The First Ecumenical Council – held in Nicaea in 325.   Convened by Emperor Constantine the Great, with 318 Bishops participating.

Arius, a priest from Alexandria, Egypt, denied the divinity of Christ.   If Jesus was born, then there was a time when he did not exist.   If he became God, then there was a time when he was not.   The Council Fathers declared Arius’ teaching a heresy, unacceptable to the Church and decreed that Christ is God, of the same essence (homoousios) with the Father.   The first seven articles of the Creed were ratified at this Council.   The major defenders of Orthodoxy present were Saints Nicholas the Wonderworker, Athanasios the Great, James of Nisibis, and Spyridon of Tremithus.

The Second Ecumenical Council – held in Constantinople in 381.  Convened by Emperor Theodosius the Great, with 150 Bishops participating.

Macedonius, somewhat like Arius, was misinterpreting the Church’s teaching on the Holy Spirit.   He taught that the Holy Spirit was not a person (hypostasis), but simply a power or dynamic of God.  Therefore the Spirit was inferior to the Father and the Son.  The Council Fathers condemned Macedonius’ teaching and defined the doctrine of the Holy Trinity, proclaiming that there is one God in Three Persons (Hypostases):  Father, Son, and Holy Spirit. The major defenders of Orthodoxy present were Saints Gregory the Theologian, who presided at the Council, Gregory of Nyssa, Cyril of Jerusalem, Meletius of Antioch, and Amphilochius of Iconium.

The Third Ecumenical Council – held in Ephesus in 431.   Convened by Emperor Theodosius II (grandson of Theodosius the Great), with 200 Bishops participating.

Nestorius taught that the Virgin Mary gave birth to a man, Jesus Christ, not to God, the Logos (the Word of God, Son of God).  The Logos only dwelled in Christ, as in a Temple.  Christ was therefore only Theophoros (the Bearer of God).  Consequently, the Virgin Mary should be called “Christotokos,” Mother of Christ, and not “Theotokos,” Mother of God.   Nestorianism overemphasized the human nature of Christ at the expense of the divine.   The Council Fathers denounced Nestorius’ teaching as erroneous.  Our Lord Jesus Christ is one Person, not two separate “people”:  the Man, Jesus Christ and the Son of God, the Logos.   The Fathers decreed that the Lord Jesus Christ is complete God and complete man, with a rational soul and body.   The Virgin Mary is “Theotokos” because she gave birth not to man but to God who became man.  The union of the two natures took place in such a fashion that one did not disturb the other.   The Fathers also declared the text of the Creed from the first two Councils to be complete and forbade any change to it.

The Fourth Ecumenical Council - held in Chalcedon, near Constantinople, in 451.  Convened by the Emperor Marcian, with 650 Bishops participating.

This Council was concerned, once again, with the nature of Jesus Christ.   The teaching arose that Christ’s human nature (less perfect) dissolved itself in his divine nature (more perfect), like a cube of sugar in a cup of water.  Thus, in reality, Christ had only one nature, the Divine.  Hence the term, “Monophysites” (“mono,” one, and “physis,” nature).   Monophysitism overemphasized the Divine nature of Christ at the expense of the human.  The Council Fathers condemned Monophysitism and proclaimed that Christ has two complete natures, the Divine and the Human, which function without confusion, are not divided nor separate, and at no time did they undergo any change.

The Fifth Ecumenical Council – held in Constantinople in 553.  Convened by Emperor Justinian the Great, with 165 Bishops participating.

This Council was called in hope of putting an end to the Nestorian and Monophysite controversies.   The Council confirmed the Church’s teaching regarding the two natures of Christ (human and divine) and condemned certain writings with Nestorian leanings.   Emperor Justinian himself confessed his Orthodox Faith when he composed the famous Church hymn, “Only Begotten Son and Word of God,” which is chanted at most Divine Liturgies.

The Sixth Ecumenical Council – held in Constantinople in 680.  Convened by Emperor Constantine IV, with 170 Bishops participating.

This Council dealt with another heresy, Monothelitism, which taught that. although Christ did have two natures (divine and human) he nevertheless acted as God only.   In other words, his divine nature made all the decisions and his human nature only acted upon them.   Hence the name Monothelitism (“mono,” one and “thelesis,” will).  The Council Fathers proclaimed:  “Christ has two natures with two activities:  as God working miracles, rising from the dead and ascending into heaven; as Man, performing the ordinary acts of daily life.  Each nature exercises its own free will.” Christ’s divine nature had a specific task to perform and so did his human nature.  Each nature performed those tasks set forth without being confused, subjected to any change or working against each other. The two distinct natures and the activities related to them were mystically united in the one Divine Person of our Lord and Savior, Jesus Christ.

The major defenders of Orthodoxy present at this Council were Saints Sophronius of Jerusalem, Maximus the Confessor, and Saint Andrew of Crete.