Basic definition of the Hypostatic Union

The Hypostatic union is a dogma of the Catholic Church. It refers to the two natures of Christ. These natures are the Divine and human which are united in one incarnated person, Jesus.

The term comes from the word Hypostasis, which means, that which lies beneath as basis or foundation. Hypostasis denotes reality as distinguished from appearances. It denotes an actual, concrete existence. Before the Council of Nicæa (325) hypostasis was synonymous with ousia (roughly meaning “being” in English). The distinction between them developed in the Church as the various heresies about Christ emerged and were debated. It was definitively established by the Council of Chalcedon (451), which declared that in Christ the two natures, each retaining its own properties, are united in one subsistence and one person. They are not joined in a moral or accidental union (as Nestorius asserted), nor commingled (as Eutyches asserted), and nevertheless they are substantially united.

Biblical Basis for the Hypostatic Union

In the first chapter of John, we have a solid basis for the understanding of the Incarnation of Christ, “In the beginning was the Word, and the Word was with God, and the Word was God.” (John 1:1). In verse 14, we hear about the incarnation of Jesus: “And the Word became flesh and made his dwelling among us” (John 1:14).

In Philippians 2:6-7, St. Paul writes about the natures of Christ: “Who, though he was in the form of God, did not regard equality with God something to be grasped. Rather, he emptied himself, taking the form of a slave, coming in human likeness; and found human in appearance”

Acts 3:15 gives us some perspective on the relationship between the human and Divine natures of Christ, “But the author of life you killed, whom God has raised from the dead: of which we are witnesses”. If Christ was killed, he must have had a human nature. He could not have been killed had he not been human, as Tertullian argues later on.

In Colossians 2:9, St. Paul tells writes, “For in him dwells the whole fullness of the deity-bodily”. Paul refers to both the human and Divine natures.

The Hypostatic Union in the Early Church

The early forms of the creed all make profession of faith, not "in one Lord Jesus Christ, the Only-begotten Son of God, Who became Man for us and was crucified" (Denzinger’s “Enchiridion”). These creeds express the 2 natures of Christ: God and man.

In his work, “Ancoratus” (the well anchored man), which includes arguments against Arianism and the teachings of Origen, Epiphanius of Salamis (? - 403) contends that even before the heresies of Nestorius, the Oriental Church proposed to catechumens a creed that was more detailed than that proposed to the faithful. This creed contained the following: "We believe . . . in one Lord Jesus Christ, the Son of God, begotten of God the Father . . . that is, of the substance of the Father . . . in Him Who for us men and for our salvation came down and was made Flesh, that is, was perfectly begotten of Mary ever Virgin by the Holy Spirit; Who became Man, that is, took perfect human nature, soul and body and mind and all whatsoever is human save only sin, without the seed of man; not in another man, but unto himself did He form Flesh into one holy unity [eis mian hagian henoteta]; not as He breathed and spoke and wrought in the prophets, but He became Man perfectly; for the Word was made Flesh, not in that It underwent a change nor in that It exchanged Its Divinity for humanity, but in that It united Its Flesh unto Its one holy totality and Divinity.”

The ante-Nicaean Fathers expressed the belief in the union of the two natures of Christ. St. Ignatius of Antioch wrote in his letter to the Ephesians, “There is only one physician — of flesh yet spiritual, born yet unbegotten, God incarnate, genuine life in the midst of death, sprung from Mary as well as God, first subject to suffering then beyond it — Jesus Christ our Lord.” St. Justin the Martyr wrote, "Since the Word is the first-born of God, He is also God"

Melito, Bishop of Sardis (about 176), wrote: "Since the same (Christ) was at the same time God and perfect Man, He made His two natures evident to us; His Divine nature by the miracles which He wrought during the three years after His baptism; His human nature by those thirty years that He first lived, during which the lowliness of the Flesh covered over and hid away all signs of the Divinity, though He was at one and the same time true and everlasting God"

St. Irenæus, contends that: "If one person suffered and another Person remained incapable of suffering; if one person was born and another Person came down upon him that was born and thereafter left him, not one person but two are proven . . . whereas the Apostle knew one only Who was born and Who suffered" Tertullian also strongly argued for Christ's two natures: "Was not God really crucified? Did He not really die as He really was crucified?"

Sources

Drum, Walter. "The Incarnation." The Catholic Encyclopedia. Vol. 7. New York: Robert Appleton Company, 1910. 4 Oct. 2012 <http://www.newadvent.org/cathen/07706b.htm>.
Pace, Edward. "Hypostatic Union." The Catholic Encyclopedia. Vol. 7. New York: Robert Appleton Company, 1910. 4 Oct. 2012 <http://www.newadvent.org/cathen/07610b.htm>.