The hypostatic union is the biblical doctrine that in the one person of Jesus there are two distinct natures: the divine and the human. Each nature retains its essence and attributes and were not lessened or changed in the person of Christ at the incarnation.  Yet, there are not two persons, but one person who is Christ.  Furthermore, the attributes of both natures were ascribed to the single person. This is called the communicatio idiomatum. It means the “communication of the attributes.” So, Jesus, who had two natures, claimed the divine attributes when he said, “Now, Father, glorify Me together with Yourself, with the glory which I had with You before the world was,” (John 17:5). He claimed human attributes when he said, “I am thirsty,” (John 19:28). So, we see that Jesus is both divine and human. He is divine so that he could offer a sacrifice of divine value. He is human so he could sacrifice for the sins of people.  Jesus is the Word made flesh (John 1:1, 14).  The Word was “joined” with humanity (Col. 2:9).  Jesus’ divine nature was not altered.

The hypostatic union was canonized at the Council of Chalcedon in 451¹Fahlbusch, E., & Bromiley, G. W. (1999-<2003). The encyclopedia of Christianity (2:675). Grand Rapids, Mich.; Leiden, Netherlands: Wm. B. Eerdmans; May 2000, page 675.  Hypostatic is derived from the Greek hypostasis and is tranlsated as “nature” in the NASB in Heb. 1:3, “And He is the radiance of His glory and the exact representation of His nature, and upholds all things by the word of His power.” It is translated as “image” in the ASV, KJV and NKJV, “imprint” in the ESV and NRSV.