Leo's letter that ended a heresy
Leo the Great's Tome
Leo I, bishop of Rome, is not able to attend the councils that are debating the nature of Christ. He is too far away, the empire is too unstable, and his administrative duties in Rome are too consuming. So he writes.
His letter to Flavian of Constantinople — written in June 449 AD, known as the Tome of Leo — is a masterpiece of theological precision. In it he articulates the orthodox position on the relationship of Christ's two natures with such clarity and balance that when it is finally read at the Council of Chalcedon two years later, the assembled bishops reportedly cry out: This is the faith of the fathers! Peter has spoken through Leo!
The Tome argues for what becomes the Chalcedonian definition: Christ is one person in two natures, the natures distinct and complete, not mixed or confused or separated or divided. The divine does not absorb the human. The human does not split off from the divine. Both are fully present in the one person.
Leo writes with the confidence of a man who believes he has simply said what the church has always believed: that the eternal Son of God took on a complete human nature — body, soul, will, emotions, limitations — without ceasing to be what he eternally is.
Fully God. Fully human. One Christ.
The formula is not a solution to the mystery. It is a boundary marker around it — a way of saying what cannot be true, so that what is true has room to be itself.
“Each nature retains without defect its proper character: and as the form of God does not take away the form of a servant, so the form of a servant does not impair the form of God.”
— Leo I, Tome to Flavian, 449 AD
“who, existing in the form of God, didn't consider it robbery to be equal with God, but emptied himself, taking the form of a servant, being made in the likeness of men.”
Leo's formula — one person, two natures, without confusion, without change, without division, without separation — is not a philosophical solution to the mystery of the incarnation. It is a refusal of the wrong solutions.
The mystery remains. What Leo gives is four fences around it, marking out the territory where the truth lives and distinguishing it from the errors on every side.
This is what doctrine does at its best: not explain the mystery but protect it from the explanations that would dissolve it.
Fully God and fully human. What does it mean to you — practically, today — that the one who saves you was both?