Every time we profess the Nicene Creed, we affirm our belief that Jesus Christ is inseparably true God and true man. "For us men and for our salvation he came down from heaven; by the power of the Holy Spirit, he became incarnate of the Virgin Mary, and was made man."

But there was a time when this teaching caused one of the greatest controversies in the Church's history, and it all swirled around a single question - was Mary truly the Mother of God?

The scene was set in 428 when a cleric named Nestorius was installed as Bishop of Constantinople. He became involved in a theological dispute between factions in the Church and the local government over whether Mary could properly be called Theotokos (Greek for Mother of God). One faction of the Church and the general public supported the title Theotokos, while the reigning aristocracy thought she should be called Anthropatokos - or "mother of man." Nestorius proposed a compromise and suggested the title Christotokos or Mother of Christ, meaning that Mary was the mother of Christ only in respect to His humanity.

But this decision was far weightier than it may first appear because if Mary was only the mother of the human Jesus, and not of the Divine Son of God, that meant Jesus Christ had to have been two separate persons. Consider just one ramification of this belief: if Jesus was two separate persons, which one died on the cross, Jesus or God? If it was Jesus the human, then the atonement is not of divine quality and would therefore be insufficient to cleanse us from our sins. In other words, determining whether Mary was the mother of God became essential for defining one of the most fundamental truths of our Faith - that Jesus Christ was both God and Man.

Known as the Hypostatic Union, the Catechism teaches that in Christ there are two natures, one divine and one human, and that these two natures are inseparably united in one Person, namely, the Second Person of the Most Holy Trinity. This most perfect union is called the Hypostatic Union (Catechism Nos. 252, 466).

As Dr. Mark Miravalle explains, "The objection of the Nestorians [followers of Nestorius] against the term Theotokos was based on a false notion of motherhood, and also of the Hypostatic Union. To understand the Catholic dogma, we must have exact ideas concerning both."

Motherhood is the relationship established when a woman communicates to her offspring a nature identical to her own, and this by means of a true generation (conception, gestation, birth), he explains. A mother is the parent of the whole person, not just the physical body. For instance, this is why we would say that St. Ann was Mary's mother. "She was the mother of Mary (i.e., this whole and complete person: Mary), and not only of Mary's body, even though we know that St. Ann did not furnish Mary's soul," Dr. Miravalle explains.

Mary did not supply Christ with either His divine nature or his divine Person because both existed from all eternity. She furnished only His human nature, but since that human nature was inseparably united to the divine Person in the very first instant of Christ's conception, we say that Mary conceived and gave birth to a Son who is truly God, and hence she is the Mother of God.

"The fact that there are two natures in Christ entails a twofold sonship. Because His divine nature was generated from the Father from all eternity, Christ is the true Son of God the Father. Because His human nature was generated from Mary, Christ is the true Son of Mary. However, this twofold sonship does not imply two Sons. Being one undivided Person, Christ the Son of the eternal Father is absolutely identical with Christ the Son of Man. Hence Mary is truly the Mother of God.

"By destroying this oneness of Christ's Person, the Nestorians were led to deny Mary's divine Motherhood. By this same token, when the Church defended and defined Mary's divine Motherhood, she was also safeguarding the revealed Catholic doctrine concerning the Hypostatic Union. They necessarily stand or fall together."

But once the compromise was struck, Nestorius began to preach his beliefs that the Virgin Mary gave birth to a man, Jesus Christ, not God, the "Logos." Eventually, his lectures were published and circulated beyond Constantinople until they reached the jurisdiction of the great Saint Cyril of Alexandria.

Saint Cyril began to preach against Nestorius and published his famous "Letter to the Monks" in which he affirmed the reality of the humanity of Christ and the singleness of His Divine Person. He spent the winter of 429 and early 430 studying Nestorius’ sermons and preparing a dossier which included extracts from Nestorius’ writings as well as extensive patristic writings supporting the belief that Mary was the Mother of God.

A copy of the dossier was sent to both the Roman Emperor Theodosius and Pope Celestine of Rome. Shortly after Pope Celestine formally condemned Nestorius' teaching, Emperor Theodosius announced a call for an ecumenical council to consider the whole issue of the Nestorian controversy. The council was to be held at Ephesus on the Pentecost of 431 (which was on June 7th that year).

Bishops began to arrive in Ephesus well before Pentecost, with Nestorius and 16 of his bishops among the first to arrive. St. Cyril arrived a few days before Pentecost with 50 bishops, but many bishops were delayed in arriving, which caused the opening of the council to be postponed for nearly three weeks. Because many of the bishops were becoming sick, and a few even died, from the hot weather and the limited facilities of the city, St. Cyril felt compelled to start the Council.

However, one of the absent bishops, John of Antioch, was a dear friend and supporter of Nestorius, so a movement began to have the council called illegitimate because it started without him. As a result, when the First Session of the Council began on Monday morning, June 22nd, at Saint Mary’s Cathedral with Saint Cyril presiding, Nestorius refused to show himself.

The proceedings went on without him. Two acquaintances of Nestorius testified that the Bishop of Constantinople had repeatedly declared that "We must not say that God is two or three months old." One of these witnesses also said that Nestorius believed the Son who died on the cross was to be distinguished from the Word of God.

The Creed of Nicea was read aloud at the Council, at which time it was declared that this was the standard faith of Orthodoxy that was to be followed. All agreed that Nestorius had blasphemed Jesus Christ and was thereafter to be excluded from "the episcopal dignity and from all priestly communion." The decree was signed by 197 bishops on June 23, 431.

A brief notification addressed to "the new Judas" was sent to Nestorius. Apparently, he refused to receive it, so the document was pegged to his door.

The people of Ephesus were overjoyed at the decision of the Council and escorted the bishops home that evening with torches and incense. "When they heard that the wretched men were deposed, they all began with one voice to cry out in praise of the Holy Council, glorifying God because the enemy of the Faith had fallen," St. Cyril described.

But the intrigues were not yet over. When John of Antioch finally arrived, he was disappointed that the Council convened without him and responded by declaring it illegal and opening his own "little council" with 43 bishops in attendance. This caused great division and lengthy debates about the legitimacy of the original Council even after it concluded, but an accord was eventually reached between Saint Cyril and St. John to accept the appellation "mother of God," and the dogma on the human and divine aspects of Jesus who was thereafter declared to be of two separate natures though perfectly united in Christ. Known as the Formula of Union, the Council stated:

“We confess then, Our Lord Jesus Christ, the only begotten Son of God, perfect God and perfect man . . . born of Mary the Virgin according to His humanity, one and the same consubstantial with the Father in Godhead and consubstantial with us in humanity, for a union of two natures took place. Therefore we confess one Christ, one Son, one Lord. According to this understanding of the unconfused union, we confess the holy Virgin to be the Mother of God because God the Word took flesh and became man and from his very conception united to Himself the temple He took from her.”