What is the one person in whom the two natures of Christ are united?

The correct answer is that the two natures of Christ are united in the Son. In Christian theology, particularly within the context of the doctrine of the Incarnation, the Son refers to Jesus Christ, who is understood to be both fully divine and fully human. This union of two distinct natures—divine and human—occurs within the one person of Jesus Christ, the Son of God.

This concept is crucial because it emphasizes that in Christ, the divine nature and the human nature coexist without mixing or altering each other. Understanding this union is fundamental to many doctrines, including salvation and the nature of the Trinity.

The other options reflect different persons of the Holy Trinity but do not encompass the union of Christ's natures in the same way. The Father represents the first person of the Trinity, the Spirit refers to the Holy Spirit, and "Man" in this context could refer to humanity in general, rather than specifically to the person of Jesus. Thus, the Son is the only option that accurately represents the theological truth regarding the union of Christ's two natures.