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What did the phrase one person in two natures mean at the Council of Chalcedon?

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Christology The Transfiguration, the nature of Jesus as the Son of God being revealed to the apostles Peter, James, and John, mosaic icon, early 13th century; in the Louvre, Paris.

At the Council of Chalcedon in 451, the phrase "one person in two natures" was established to define the hypostatic union, affirming that Jesus Christ is simultaneously perfect in deity and perfect in humanity.12

This doctrine asserts that Christ exists in two natures—divine and human—that are united without being "mixed, transmuted, divided, or separated". The council emphasized that the union does not eliminate the distinction between the two natures; rather, the identity of each is preserved while they concur into a single person and being.2

This formulation was designed to resolve long-standing theological controversies by rejecting two extremes:
* Nestorianism: Which was accused of splitting Christ into two separate persons.13
* Monophysitism: Which held that Christ possessed only a single, divine nature, effectively absorbing his humanity.124

By affirming both the unity of Christ’s person and the distinctness of his two natures, the council provided a normative statement for the Christian doctrine of the person of Christ, ensuring that his full divinity and full humanity remain essential to the faith.12