In theology, we call the act of God becoming man the “Incarnation,” (the act of being made flesh). The Incarnation is the act of the Second Person of the Blessed Trinity coming to the earth as a true man by assuming human nature in the womb of Mary. As man, He loses none of His divinity but rather chooses to cloak it, or as St. Paul says, he “emptied Himself, taking the form of a servant” (Phil. 2:7).
“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.” (CCC 464)