The doctrine of the Incarnation of Christ is central to the traditional Christian faith as held by the Catholic Church, the Eastern Orthodox Church, and all Protestants.
Briefly, it is the belief that the Second Person of the Christian Godhead, also known as the Son or the Logos (Word), "became flesh" when he was miraculously conceived in the womb of the Virgin Mary. In the Incarnation, the divine nature of the Son was perfectly united with human nature in one divine Person. This person, Jesus Christ, was both truly God and truly man. Jehovah's Witnesses, however, believe that Jesus was the Son of God, but not truly God. The incarnation is commemorated and celebrated each year at the Feast of the Incarnation, also known as Annunciation.
The Athanasian Creed contains what may be considered a comprehensive definition of the Incarnation.
The Athanasian Creed (Quicumque vult) is a statement of Christian doctrine traditionally ascribed to St. Athanasius, Archbishop of Alexandria, who lived in the 4th century. However most of today's historians agree that in all probability it was originally written in Latin, not in Greek, and probably originated in Gaul around 500; if so, then Athanasius cannot have been the original author. Its theology is closely akin to that found in the writing of Western theologians, especially Ss. Ambrose of Milan, Augustine of Hippo, and Vincent of Lérins. J.N.D. Kelly, a contemporary patristics scholar, believes that St. Vincent of Lérin may have been its author (J.N.D. Kelly, The Athanasian Creed, NY: Harper and Row, 1964).
It was designed to overcome Arianism, Nestorianism, Monophysitism, and Macedonianism. The filioque is part of its original text. Liturgically, this Creed was recited at the Sunday Office of Prime in the Western Church; it is not used in the Eastern Church.
Today the Athanasian Creed is rarely used even in the Western Church. When used, one common practice is to use it once a year on Trinity Sunday.
The ICET English Language Translation
The following translation was prepared by the International Consultation on English Texts:
Whoever wants to be saved should above all cling to the catholic faith.
Whoever does not guard it whole and inviolable will doubtless perish eternally.
Now this is the catholic faith: We worship one God in trinity and the Trinity in unity, neither confusing the persons nor dividing the divine being.
For the Father is one person, the Son is another, and the Spirit is still another.
But the deity of the Father, Son, and Holy Spirit is one, equal in glory, coeternal in majesty.
What the Father is, the Son is, and so is the Holy Spirit.
Uncreated is the Father; uncreated is the Son; uncreated is the Spirit.
The Father is infinite; the Son is infinite; the Holy Spirit is infinite.
Eternal is the Father; eternal is the Son; eternal is the Spirit:
And yet there are not three eternal beings, but one who is eternal;
as there are not three uncreated and unlimited beings, but one who is uncreated and unlimited.
Almighty is the Father; almighty is the Son; almighty is the Spirit:
And yet there are not three almighty beings, but one who is almighty.
Thus the Father is God; the Son is God; the Holy Spirit is God:
And yet there are not three gods, but one God.
Thus the Father is Lord; the Son is Lord; the Holy Spirit is Lord:
And yet there are not three lords, but one Lord.
As Christian truth compels us to acknowledge each distinct person as God and Lord, so catholic religion forbids us to say that there are three gods or lords.
The Father was neither made nor created nor begotten;
the Son was neither made nor created, but was alone begotten of the Father;
the Spirit was neither made nor created, but is proceeding from the Father and the Son.
Thus there is one Father, not three fathers; one Son, not three sons; one Holy Spirit, not three spirits.
And in this Trinity, no one is before or after, greater or less than the other;
but all three persons are in themselves, coeternal and coequal; and so we must worship the Trinity in unity and the one God in three persons.
Whoever wants to be saved should think thus about the Trinity.
It is necessary for eternal salvation that one also faithfully believe that our Lord Jesus Christ became flesh.
For this is the true faith that we believe and confess: That our Lord Jesus Christ, God's Son, is both God and man.
He is God, begotten before all worlds from the being of the Father, and he is man, born in the world from the being of his mother --
existing fully as God, and fully as man with a rational soul and a human body;
equal to the Father in divinity, subordinate to the Father in humanity.
Although he is God and man, he is not divided, but is one Christ.
He is united because God has taken humanity into himself; he does not transform deity into humanity.
He is completely one in the unity of his person, without confusing his natures.
For as the rational soul and body are one person, so the one Christ is God and man.
He suffered death for our salvation.
He descended into hell and rose again from the dead.
He ascended into heaven and is seated at the right hand of the Father.
He will come again to judge the living and the dead.
At his coming all people shall rise bodily to give an account of their own deeds.
Those who have done good will enter eternal life,
those who have done evil will enter eternal fire.
This is the catholic faith. One cannot be saved without believing this firmly and faithfully.