Definition

The doctrine of the person of Christ confesses that the eternal Son of God, the second person of the Holy Trinity, in the fullness of time took to himself a true and complete human nature, so that in one person there are now two whole and distinct natures, the divine and the human, united without confusion, change, division, or separation. This is the hypostatic union — the joining of two natures (Greek physeis) in one person or hypostasis. The Son who is “very and eternal God” became also “very man,” and yet remained one Christ, “the only Mediator between God and man” (cf. WCF 8.2). He is not two persons, nor one person with one blended nature, but a single divine person subsisting in two unconfused natures. This is the confession of the apostle that the Word “became flesh” (John 1:14) while remaining the Word who “was God” (John 1:1), and it is the heart of the catholic and Reformed faith concerning our Lord.

Why It Matters

The whole efficacy of our salvation depends upon the constitution of the Redeemer’s person. The ancient maxim of Gregory of Nazianzus holds: “that which he has not assumed he has not healed.” If the Son did not take a true human body and a reasonable human soul, then our bodies and souls are not redeemed. If he is not truly God, then his obedience and suffering, however excellent, would be the finite work of a creature and could not bear the infinite weight of divine justice or merit eternal life for a countless multitude. The dignity of his divine person is what gives his human work its infinite value. Thus the Mediator must be both God and man, and both in one person, that the same Christ who is able to satisfy may be the very one who, being our kinsman, is obligated to obey and suffer in our stead. To get the person of Christ wrong is to lose the gospel; to confess him rightly is to find the firm ground of all assurance.

Biblical Foundation

Scripture everywhere presents Christ as one who is at once truly divine and truly human. His deity is affirmed in the opening of John’s Gospel:

“In the beginning was the Word, and the Word was with God, and the Word was God.” (John 1:1)

He is the Creator of all things, in whom “all things hold together” (Colossians 1:16-17), the radiance of the glory of God and the exact imprint of his nature (cf. Hebrews 1:3), worshiped by angels and addressed as God: “Your throne, O God, is forever and ever” (Hebrews 1:8). Thomas confesses him as “My Lord and my God!” (John 20:28), and Paul declares that “in him the whole fullness of deity dwells bodily” (Colossians 2:9).

Yet the same Christ is genuinely human. The Word “became flesh and dwelt among us” (John 1:14). He was born of a woman, born under the law (cf. Galatians 4:4). He grew and “increased in wisdom and in stature” (Luke 2:52). He hungered, thirsted, wearied, wept, and slept. He “partook of” flesh and blood (Hebrews 2:14) and was made like his brothers in every respect, yet without sin. The unity of the two in one person is signaled by the way Scripture predicates the actions and titles of both natures of the single subject: the Lord of glory was crucified (cf. 1 Corinthians 2:8), and God obtained the church “with his own blood” (Acts 20:28). The supreme statement of the descent and ascent of this one person is Philippians 2:5-11, where he who was “in the form of God” took “the form of a servant” and was “born in the likeness of men.”

Key Components & Distinctions

The Incarnation

The incarnation is the act by which the eternal Son, without ceasing to be what he was, became what he was not, assuming a true human nature into union with his divine person. It was the person of the Son, not the divine nature or essence as such, that became incarnate; the Father did not become man, nor the Spirit, but the Son alone. The human nature he assumed was conceived by the power of the Holy Spirit in the womb of the virgin Mary, so that he was true man yet without inheriting the corruption of original sin. The Son took a complete humanity — a true body and a reasonable soul — “with all the essential properties, and common infirmities thereof, yet without sin” (cf. WCF 8.2). The incarnation is not a temporary visitation but a permanent assumption: the Son remains incarnate forever, the glorified God-man at the right hand of the Father.

The Hypostatic Union

The hypostatic union names the manner of the joining. The two natures are united not by mixture, nor by mere moral agreement, nor by the indwelling of God in a separate human person, but in the single divine person of the Son. The human nature has no independent personhood of its own; it subsists in the person of the Word (the doctrine of anhypostasia and enhypostasia: the human nature is not impersonal, but personalized in the Logos). Therefore there is one acting subject, one “I,” in Jesus Christ. When he speaks, suffers, obeys, and reigns, it is always the one divine person doing so, now according to one nature, now according to the other.

The Two Natures (Chalcedon)

The Council of Chalcedon (451) gave the church its enduring grammar with four negations. The two natures are joined:

• without confusion — they are not blended into a third kind of nature;
• without change — the deity is not converted into flesh, nor the flesh into deity;
• without division — the natures do not constitute two persons;
• without separation — the union is real and permanent, never sundered.

Each nature retains its own properties entire. The divine nature remains omnipotent, omniscient, omnipresent, immutable, and impassible; the human nature remains finite, localized, capable of growth, suffering, and death. The Reformed have guarded this with the extra Calvinisticum: even in the incarnation the Son was not confined within the human nature but continued to fill heaven and earth, “for in him all things hold together” (Colossians 1:17).

The Communicatio Idiomatum

The communication of properties is the principle that, because of the unity of the person, the attributes and actions proper to either nature may be ascribed to the one person under any of his titles. Thus Scripture can say that the Son of Man was in heaven, or that the Lord of glory was crucified, or that God purchased the church with his blood. Reformed orthodoxy carefully limits this to the person: the properties of one nature are not literally transferred into the other nature. Omnipresence is not poured into the body, nor mortality into the deity. The communication is to the concrete person, who is both, not from one abstract nature to the other. This guards against the Lutheran tendency toward the ubiquity of Christ’s body and preserves the integrity of each nature confessed at Chalcedon.

Historical Development

The church’s confession of Christ’s person was forged through successive controversies. Against early Docetism, which denied the reality of the flesh, the apostle John insisted that anyone who does not confess Jesus Christ “come in the flesh” is not of God (cf. 1 John 4:2-3). The Nicene crisis settled his full deity against Arius, confessing the Son homoousios, “of one substance with the Father” (Nicaea, 325; Constantinople, 381). Apollinaris then denied Christ a human rational soul, substituting the Logos for the human mind; he was condemned, for a soulless humanity is no true humanity. Nestorius so emphasized the distinction of natures that he seemed to divide Christ into two persons and balked at calling Mary Theotokos; the Council of Ephesus (431) affirmed that the one born of Mary is truly God the Son. Eutyches, overreacting, taught that after the union there was but one nature, the human swallowed up in the divine; the Council of Chalcedon (451) condemned this and gave the definitive statement of one person in two natures. The Reformation received this catholic settlement intact. Calvin and the Reformed orthodox developed the extra Calvinisticum in distinction from Lutheran ubiquity, and refined the doctrine of the communicatio idiomatum to preserve the unconfused integrity of the natures.

The Reformed & Confessional Position

The Westminster Confession states the doctrine with precision:

“The Son of God, the second person in the Trinity, being very and eternal God, of one substance and equal with the Father, did, when the fullness of time was come, take upon him man’s nature, with all the essential properties, and common infirmities thereof, yet without sin: being conceived by the power of the Holy Ghost, in the womb of the Virgin Mary, of her substance. So that two whole, perfect, and distinct natures, the Godhead and the manhood, were inseparably joined together in one person, without conversion, composition, or confusion. Which person is very God, and very man, yet one Christ, the only Mediator between God and man.” (WCF 8.2)

The Larger Catechism explains the necessity of both natures. It teaches that the Mediator must be God:

“It was requisite that the Mediator should be God, that he might sustain and keep the human nature from sinking under the infinite wrath of God, and the power of death; give worth and efficacy to his sufferings, obedience, and intercession; and to satisfy God’s justice, procure his favour, purchase a peculiar people, give his Spirit to them, conquer all their enemies, and bring them to everlasting salvation.” (WLC 38)

And that he must be man:

“It was requisite that the Mediator should be man, that he might advance our nature, perform obedience to the law, suffer and make intercession for us in our nature, have a fellow-feeling of our infirmities; that we might receive the adoption of sons, and have comfort and access with boldness unto the throne of grace.” (WLC 39)

And that he must be both in one person:

“It was requisite that the Mediator, who was to reconcile God and man, should himself be both God and man, and this in one person, that the proper works of each nature might be accepted of God for us, and relied on by us, as the works of the whole person.” (WLC 40)

The Shorter Catechism distills it: “The only Redeemer of God’s elect is the Lord Jesus Christ, who, being the eternal Son of God, became man, and so was, and continueth to be, God and man in two distinct natures, and one person, for ever.” (WSC 21)

Contrasting Views

The historic heresies remain the chief contrast, for each denies some essential element of the confession. Arianism denies the full deity of the Son, making him a creature; against this stands John 1:1 and the Nicene homoousios. Apollinarianism denies Christ a complete human nature by removing the human soul; against this stands the principle that the unassumed is unhealed, and the Scriptures that show Christ growing in wisdom and possessing a human will (cf. Luke 22:42). Nestorianism so divides the natures as to imperil the unity of the person, effectively positing two sons; against this stands the truth that the one born of Mary is Theotokos, God the Son. Eutychianism (monophysitism) so confuses the natures that the humanity is absorbed, yielding a single mingled nature; against this stands the abiding distinction of the natures, “without confusion.” The Lutheran doctrine of the ubiquity of Christ’s human body, while orthodox in confessing two natures, presses the communicatio idiomatum too far by ascribing the divine attribute of omnipresence to the human flesh; the Reformed, with the extra Calvinisticum, hold that the omnipresent Son fills all things according to his deity while his body remains locally in heaven.

Connections to Other Loci

The person of Christ rests upon the doctrine of the Trinity, for the incarnate One is the eternal second person, distinct from the Father and the Spirit yet of one essence with them. It depends upon Theology Proper, for only because the Son possesses the full divine essence can he be the object of worship and the source of infinite merit. It engages anthropology, for in assuming our nature Christ shows us what humanity was meant to be and becomes the last Adam. It grounds the entire doctrine of the atonement and justification, since only the God-man can satisfy divine justice and clothe us in a righteousness of infinite worth. And it undergirds eschatology, for the glorified God-man will return to raise and judge. Rightly to confess Christ’s person is to hold the keystone that locks the whole arch of Christian doctrine together.

Christ & the Gospel at the Center

The doctrine of Christ’s person is not a cold metaphysical scaffold but the warm heart of the gospel. The good news is that the eternal Son did not consider equality with God a thing to be grasped but emptied himself, taking our nature, that as one of us he might redeem us. Because he is truly man, he is our brother, our kinsman-redeemer, able to obey and suffer in our place and to sympathize with our weakness. Because he is truly God, his single act of obedience avails for multitudes and his blood is of infinite worth. Because he is one person, all that he did he did for us as a whole — the obedience of the man is the obedience of the Son of God, accepted by the Father on our behalf. The mystery of godliness is great: “He was manifested in the flesh” (cf. 1 Timothy 3:16) — and in that manifestation our salvation is secured.

Pastoral & Practical Significance

The believer draws unfailing comfort from the person of Christ. Tempted, we have a High Priest who has been “tempted as we are, yet without sin” (cf. Hebrews 4:15), and so we may “with confidence draw near to the throne of grace” (Hebrews 4:16). Grieving, we have one who wept at the tomb of his friend. Dying, we have one who has tasted death and abolished its sting. The union of natures assures us that the God who seems so high has drawn so near; the friend who walks with us is the very Lord who upholds the universe. In every trial the saint may rest in this: the One who intercedes for me is my brother in the flesh and my God in glory, and he will never let me go. To contemplate his person is to be melted into worship and steadied in hope.

Key Terms

• Hypostatic union — the union of the divine and human natures in the one person (hypostasis) of the Son.
• Incarnation — the Son’s assumption of a true human nature into his divine person.
• Anhypostasia / enhypostasia — the human nature has no independent personhood but subsists in (is personalized by) the person of the Logos.
• Communicatio idiomatum — the predicating of the properties of either nature to the one person.
• Extra Calvinisticum — the teaching that the Son, even incarnate, continues to fill all things beyond the flesh.
• Theotokos — “God-bearer,” affirming that the one Mary bore is God the Son.
• Homoousios — “of the same substance,” the Nicene term for the Son’s equality with the Father.

Key Scripture References

• John 1:1, 14 — the Word who was God became flesh.
• John 20:28 — “My Lord and my God!”
• Philippians 2:5-11 — the descent and exaltation of the one person.
• Colossians 1:15-20; 2:9 — Creator and Reconciler, the fullness of deity bodily.
• Hebrews 1:1-3, 8 — the Son upholding all things, addressed as God.
• Hebrews 2:14-18; 4:15 — true partaker of flesh and blood, tempted yet sinless.
• Galatians 4:4 — born of woman, born under the law.
• 1 Timothy 2:5 — one Mediator, the man Christ Jesus.

Further Study

• Westminster Confession of Faith 8.2; Larger Catechism Q. 36-40; Shorter Catechism Q. 21-22.
• The Definition of Chalcedon (451); the Nicene-Constantinopolitan Creed (381).
• John Calvin, Institutes, Book II, chapters 12-14.
• Gregory of Nazianzus, Epistle 101 (on Apollinarianism).
• Companion guides: Christology Overview, The Offices of Christ, The Atonement.