In our study of the person of Christ, we have seen that although some groups denied the true deity of Christ during the early centuries of church history, the church had largely settled the question of our Savior’s divinity by the end of the fourth century. Scripture’s teaching on the deity of Christ in passages such as John 1:1–14 is clear, so the church could affirm the full deity of our Lord against the Arians and other groups. At the end of the fourth century and into the fifth century, however, debate was ongoing regarding the relationship of the deity of Christ to the humanity of Christ. Everyone agreed that Christ is in some sense both divine and human, but different positions were held regarding the nature of our Lord’s humanity and how it is united to His deity in His person.
These disagreements led to the Council of Chalcedon in 451. Chalcedon affirmed the Christology of Cyril of Alexandria and of Leo the Great, who was the bishop of Rome at the time. It condemned Nestorianism, Eutychianism, and every heresy that denies the true humanity and true deity of Christ and their true union in the one divine person of the Son of God. Chalcedon also gave us the standard orthodox definition of the person of Christ, which says that in the one person of Christ are perfectly united the divine nature and a human nature, and that this union is without confusion, mixture, separation, or division, each nature retaining its own attributes. This is what is called the hypostatic union: Christ is one person with two natures.
The Definition of Chalcedon does not spell out this union in every detail, but it gives parameters to preserve the biblical witness. Because each nature retains its own attributes, Christ is truly human and truly divine. He is not one at the expense of the other, and because these natures are not confused or mixed, He is not a third kind of being, neither truly human nor truly divine. The natures are united in one person without separation or division, so Christ is a single person or subject, a point Chalcedon emphasizes by repeatedly speaking of “one and the same” Christ. He may act according to His divine nature or according to His human nature, but the same Christ acts no matter whether He is exercising His divine attributes or His human attributes.
The unity of the natures in the one person means that the attributes of each nature belong to the person. Christ’s divine nature, for example, does not have blood, but the person of Christ does because a human nature belongs to Christ (Acts 20:28).
Who upholds the cosmos? Christ, according to His divine nature, because deity sustains the creation. Who died and rose again? Christ, according to His human nature, because only humanity can die and be restored to life. We distinguish Christ’s two natures, but we do not separate them. If we separate them or if we fail to distinguish them, we commit error. By knowing the Definition of Chalcedon, we preserve biblical truth and can teach it to others.