464 The unique and altogether singular event of the Incarnation of the Son of God does not mean that Jesus Christ is part God and part man, nor does it imply that he is the result of a confused mixture of the divine and the human. He became truly man while remaining truly God. Jesus Christ is true God and true man. During the first centuries, the Church had to defend and clarify this truth of faith against the heresies that falsified it.
467 ….the fourth ecumenical council, at Chalcedon in 451, confessed:
Following the holy Fathers, we unanimously teach and confess 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, composed of rational soul and body; consubstantial with the Father as to his divinity and consubstantial with us as to his humanity; “like us in all things but sin.” He was begotten from the Father before all ages as to his divinity and in these last days, for us and for our salvation, was born as to his humanity of the virgin Mary, the Mother of God.1
We confess that one and the same Christ, Lord, and only–begotten Son, is to be acknowledged in two natures without confusion, change, division, or separation. The distinction between the natures was never abolished by their union, but rather the character proper to each of the two natures was preserved as they came together in one person (prosopon) and one hypostasis.2
469 The Church thus confesses that Jesus is inseparably true God and true man. He is truly the Son of God who, without ceasing to be God and Lord, became a man and our brother:
“What he was, he remained and what he was not, he assumed,” sings the Roman Liturgy.3 And the liturgy of St. John Chrysostom proclaims and sings: “O only–begotten Son and Word of God, immortal being, you who deigned for our salvation to become incarnate of the holy Mother of God and ever–virgin Mary, you who without change became man and were crucified, O Christ our God, you who by your death have crushed death, you who are one of the Holy Trinity, glorified with the Father and the Holy Spirit, save us!”4
For more, read paragraphs 456-483 here: http://www.usccb.org/beliefs-and-teachings/what-we-believe/catechism/catechism-of-the-catholic-church/epub/index.cfm
1. Council ofChalcedon(451): DS 301; cf Heb 4:15
2. Council ofChalcedon: DS 302
3. LH, January 1, Antiphon for Morning Prayer; cf St. Leo the Great, Sermo in nat. Dom. 1,2; PL 54, 191-192
4. Liturgy of St.John Chrysostom, Troparion “O monogenes.”
Excerpts from the English translation of the Catechism of the Catholic Church for use in the United States of America Copyright © 1994, United States Catholic Conference, Inc. – Libreria Editrice Vaticana. Used with Permission.