Catechism of the Catholic Church

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. (88)