Misconceptions concerning the nature of Christ arose during the early centuries of the Christian era.

The Gnostics believed that matter was an emanation of an evil principle, therefore, the Word could not have assumed a human body but only an apparent one or an astral body. St. John the apostle was faced with this same heresy because he wrote, "Beloved, do not trust every spirit but test the spirits to see whether they belong to God, because many false prophets have gone out into the world. This is how you can know the Spirit of God: every spirit that acknowledges Jesus Christ come in the flesh belongs to God, and every spirit that does not acknowledge Jesus does not belong to God." (1Jn 4:1-3) As a consequence some Gnostics concluded that since Christ had descended from heaven in a spirit form body he had passed through Mary without appropriating anything from her body, like water passing through a canal. Further, since he did not have a true human body he only appeared to suffer and die on the cross. In other words, mankind was not saved by Christ suffering, death and resurrection. Gnostics believe that they have secret knowledge about God, humanity and the rest of the universe of which the general population was unaware. Their interpretation of Scripture is based on the Gospel of Thomas, a non-canonical book.

Arius (306) who was a priest in the church of Alexandria taught that Christ had a human body but no human soul. He believed that the Logos (Word) substituted for Christ's soul. Arius also maintained that Christ was like God but a creature created by the Father through whom He made the universe. This error was so widespread and caused much consternation and disunity in the Roman Empire. Constantine called the Council of Nicea (325) which declared that Christ as God was of the same substance as the Father.

Nestorius became patriarch of Constantinople (428) and taught that there were not only two natures in Christ, a human and a divine nature but also two persons or identities. The man Christ is not God, but a bearer of God, that is the divine Logos resided in the man in the same way that that God dwells in the just. Consequently, Mary was not the mother of God but only of the man Jesus. The Church, however, held that the two natures were united in one person, the divine person and that Mary conceived and gave birth to the whole Christ thereby she is the Mother of God. Nestrorius was deposed by the Council of Ephesus in 431 with the following words: "Our lord Jesus Christ, who has been blasphemed by him, has determined through this most holy synod that the same Nestorius should be stripped of his Episcopal dignity and removed from the college of priests."

Another heresy in the 5th century began with Eutyches, a priest of Constantinople and his followers. They presumed that that the human nature of Christ had been transformed or absorbed by the divine nature. Some even imagined that the two natures of Christ were mixed, thereby giving rise to a different nature.

Flavian, Patriarch of Constantinople presented the case to Pope Leo I (the Great) in 449), the same pope who who convinced Attila the Hun to spare Rome in 452. The Pope defined the truth about Christ's nature in Letter 28, the Tone, addressed to the Patriarch.

Pope Leo wrote that Eutyches has fallen into error due to ignorance and presumption, because his reasoning was not based on the whole of scripture nor did he pay attention to the Creed. The Pope made the following observations:

1)The nativity of Christ took nothing and added nothing to his eternal birth.
2) The Holy Spirit imparted fertility to the Virgin, yet a real body was received from her body.
3) Both natures of Christ, the divine and human retained their proper character. The form of God did not do away with his human nature, not did the form of man impair his divine nature.
The Pope did not define something new but explained the truth found in Scripture and Tradition.

Finally, in 451 the Council of Chalsedon define clearly what is to be believed about the nature of Christ which reflects much of what Pope Leo the Great had written in the Letter 28, mentioned above.

"So, following the saintly fathers, we all with one voice teach the confession of one and the same Son, our Lord Jesus Christ: the same perfect in divinity and perfect in humanity, the same truly God and truly man, of a rational soul and a body; consubstantial with the Father as regards his divinity, and the same consubstantial with us as regards his humanity; like us in all respects except for sin; begotten before the ages from the Father as regards his divinity, and in the last days the same for us and for our salvation from Mary, the virgin God-bearer as regards his humanity; one and the same Christ, Son, Lord, only-begotten, acknowledged in two natures which undergo no confusion, no change, no division, no separation; at no point was the difference between the natures taken away through the union, but rather the property of both natures is preserved and comes together into a single person and a single subsistent being; he is not parted or divided into two persons, but is one and the same only-begotten Son, God, Word, Lord Jesus Christ, just as the prophets taught from the beginning about him, and as the Lord Jesus Christ himself instructed us, and as the creed of the fathers handed it down to us."

But, this is not the end of the story. In the seventh century Patriarch Sergius or Constantinople promulgated the idea that in Christ there were two natures but one divine will in the hope that the Monophysites could agree that Jesus had two natures if he only had one will. Even Pope Honorius favored Monothelitism which goes to show that the opinion of a pope is not infallible. The words of Christ in more than one passage imply a human and divine will, e.g. "I came down from heaven not to do my own will but the will of the one who sent me." (Jn 6:38) Christ human will was always subordinated to to the divine will. The Sixth Ecumenical Council in Constantinople concluded that "Although joined together[in Christ] yet each nature wills and does the things proper to it and that indivisibly and inconfusedly. Wherefore we confess two wills and two operations, concurring most fitly in him for the salvation of the human race."

6. What is A Dogma?