The unity of Christ is the doctrine that Jesus, although he possesses two distinct and complete natures—he is simultaneously fully God and fully man—is nevertheless one integral person, God the Son incarnate.

The incarnation of the person of the eternal Son as Jesus Christ is one of the great mysteries of the Christian faith. This personal incarnation, in which “the Word became flesh” (John 1:14), is often referred to as the “hypostatic union” (after the Greek word hypostasis, which came to function in the patristic era as a technical term for a “person”).

The Bible affirms repeatedly that Christ is fully God, speaking even of “the church of God, which he obtained with his own blood” (Acts 20:28). He is the “image of the invisible God,” the one through whom and for whom “all things were created,” and in whom “all things hold together” (Col 1:15–18). He is “the exact imprint of [God’s] nature” (Heb 1:3), and is addressed by God as God: “Your throne, O God, is forever and ever” (Heb 1:8). Before his incarnation (and during it), he had “equality with God” (Phil 2:6).

The Bible also affirms repeatedly that Christ is fully man, speaking of “the man Christ Jesus” (1 Tim 2:5) and the Word who “became flesh and dwelt among us” (John 1:14). “Though he was in the form of God … [he] emptied himself, by taking the form of a servant, being born in the likeness of men,” Paul says, “and being found in human form,” he did what only a human can do: “he humbled himself by becoming obedient to the point of death, even death on a cross” (Phil 2:6–8).