Today, November 10, is the Feast of Leo the Great (Bishop of Rome 440-461). He was involved in one of the great Christological controversies. The question dealt with the relationship of divinity and humanity in Christ. Eutyches argued a form of monophysitism, the idea the Christ has only one nature. He conflated the two natures in Christ arguing that there was only one nature “after the union” in the one person of Christ. Further he denied that Christ’s humanity is consubstantial with ours. In 449 Leo wrote a letter, known as the Tome of Leo to Bishop Flavian of Constantinople, in which he affirmed that Christ has two natures, one human and one divine, that the two natures exist in one person, and that Christ’s human nature is consubstantial with our humanity. The letter was read in 451 by the Council of Chalcedon and judged by them to be sound doctrine. It contributed much to the creedal statements of that council.
Here is an excerpt from Leo’s tome:
So without leaving his Father’s glory behind, the Son of God comes down from his heavenly throne and enters the depths of our world, born in an unprecedented order by an unprecedented kind of birth. In an unprecedented order, because one who is invisible at his own level was made visible at ours. The ungraspable willed to be grasped. Whilst remaining pre-existent, he begins to exist in time. The Lord of the universe veiled his measureless majesty and took on a servant’s form. The God who knew no suffering did not despise becoming a suffering man, and, deathless as he is, to be subject to the laws of death. By an unprecedented kind of birth, because it was inviolable virginity which supplied the material flesh without experiencing sexual desire. What was taken from the mother of the Lord was the nature without the guilt [of original sin]. And the fact that the birth was miraculous does not imply that in the Lord Jesus Christ, born from the virgin’s womb, the nature is different from ours. The same one is true God and true man.
Collect from the Book of Common Prayer
O Lord our God, grant that your Church, following the teaching of your servant Leo of Rome, may hold fast the great mystery of our redemption, and adore the one Christ, true God and true Man, neither divided from our human nature nor separate from your divine Being; through Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, now and for ever. Amen.