Question: "What was the significance of the Council of Chalcedon?"
Answer: The Council of Chalcedon met in AD 451 in Chalcedon, a city in Asia Minor. The council’s ruling was an important step in further clarifying the nature of Christ and the orthodox doctrine of the Trinity. The council also laid the groundwork for one of the most significant events in ecclesiastical history—the Great Schism.
In order to appreciate the significance of the Council of Chalcedon, we need a little background. Debate about the person of Christ arose prior to the first Council of Nicaea in AD 325. A man named Arius had taught the false doctrine that the Son of God was a created being and that He was of a different substance (heteroousios) than the Father. The Council of Nicaea sought to unambiguously define the relationship between the Father and the Son. The council said Jesus was truly God. Yet the opponents of the deity of Christ did not simply give up after the Nicene affirmation. But faithful Christians like Athanasius continued to defend Christ’s deity, and, in the end, truth triumphed over error.
After Nicaea came the Council of Constantinople in AD 381, which rejected the teachings of Apollinaris, who said that Jesus’ divine nature had displaced His human mind and will. According to Apollinaris Jesus was not fully human, a teaching that 2 John 1:7 warns against. Later, Nestorius said Jesus had two separate natures and two wills, essentially making Him two persons sharing one body. This teaching was condemned at the Council of Ephesus in AD 431. And ten years later Eutyches also denied that Jesus was truly human, saying Jesus’ human nature was “absorbed” or swallowed up by His divine nature. This led to the Council of Chalcedon, which only lasted from October 8 to November 1, 451.
The Council of Chalcedon anathematized (cursed) those who taught that Christ had only a single, divine nature and those who taught a “mixture” of His two natures. The Council produced the “Chalcedonian Definition,” which affirms that Christ is “the same perfect in Godhead and also perfect in manhood; truly God and truly man.” He is “consubstantial [homoousios] with the Father according to the Godhead, and consubstantial with us according to the Manhood.” Jesus Christ is to be “to be acknowledged in two natures, inconfusedly, unchangeably, indivisibly, inseparably” (quoted from www.carm.org). The divine and human natures of Christ are distinct yet united in one Person. This co-existence of Christ’s two natures is called the hypostatic union.
By affirming that Jesus Christ is one Person who is both divine and human, the Council of Chalcedon made it easier to identify error. The Chalcedonian Definition affirms the truth that Jesus Christ is fully divine and, at the same time, fully human. He is both the Son of God (1 John 5:10) and the Son of Man (Mark 14:21). Jesus, the Word incarnate, assumed perfect humanity in order to save fallen humanity. He could not have saved us unless he was fully God and fully man.
The Council of Chalcedon was also significant because it ratified the creeds of Nicaea and Constantinople. And it condemned the false doctrines of Nestorius and Eutyches. The council affirmed the single personality of Christ and the authenticity and perfection of both His natures, human and divine.
Besides dealing with matters of theology, the Council of Chalcedon is famous for upholding an earlier ruling concerning church structure. The Council of Chalcedon assigned equal honor to the Church of Constantinople as the Church of Rome. The council gave the title “patriarch” to the most prominent bishops and concluded that the church of Constantinople (“New Rome”) held a position of authority similar to that of “Old Rome.” The pope, of course, rejected that particular article, while accepting the rest of the Chalcedonian Creed. Eventually, the rift between Rome and Constantinople led to the Great Schism between the Eastern Church and the Western Church in AD 1054.