The Fifth Ecumenical Council (the Second Council of Constantinople) met in 553 and reaffirmed the Christology of Ephesus and Chalcedon. Even though this council met more than a century after Cyril’s death, his influence shows in the council’s official documents. In its doctrinal declarations, the council defended the orthodoxy of the most controversial portion of Cyril’s third letter to Nestorius (the so-called twelve chapters or twelve anathemas). In short, the doctrine of Christ found in the writings of Cyril and hammered out during his controversy with Nestorius is the doctrine of Christ defended and taught in the dogmatic teaching of three ecumenical councils.
The influence of Cyril on orthodox Christology becomes even clearer when we compare the well-known penultimate paragraph of the Definition of Chalcedon with the writings of Cyril himself. For example, in his first letter to Succensus, Cyril writes, “We unite the Word of God the Father to the holy flesh endowed with a rational soul, in an ineffable way that transcends understanding, without confusion, without change, and without alteration, and we thereby confess One Son and Christ.” Cyril uses the adverbs asynchytōs, atreptōs, and ametablētos. The first of these words means “unconfused” or “distinct.” The other two words are basically synonymous and mean “immutable” or “unchangeable.” The Definition of Chalcedon teaches that the two natures are united in the one person of Christ “unconfusedly, unalterably, undividedly, inseparably.” The adverbs used are asynchytōs, atreptōs, adiairetōs, and achoristōs. The first two are identical to the first two adverbs Cyril used. It appears that Chalcedon left out the word ametablētos because it is synonymous with atreptōs. These first two words are used by Chalcedon to refute Eutychianism (the idea that the human nature and divine nature are mixed together in the one person of Christ without preserving their distinctions). The last two adverbs used by Chalcedon, while not used in Cyril’s sentence in the letter to Succensus, sum up everything Cyril ever wrote against Nestorius. Cyril repeatedly argued against Nestorius that the two natures in Christ are united “without division” and “without separation.” The words adiairetōs and achoristōs express that basic Cyrillian idea concisely. Chalcedon also affirmed Cyril’s doctrine of hypostatic union and his use of the title theotokos.
It is not an exaggeration to say that if you look to the Definition of Chalcedon (as well as to the Council of Ephesus and the Second Council of Constantinople) for the contours of your Christology, then you are looking to Cyril of Alexandria for the contours of your Christology. These three ecumenical councils viewed Cyril’s teaching as the most accurate expression of the Christology found in the Scriptures. They relied on Cyril’s works to help them express precisely the parameters of orthodoxy. This is why Cyril of Alexandria may be the most important church father many Christians have never heard of.
There truly is nothing new under the sun, and the same errors that plagued the church during the fourth and fifth centuries continue to plague the church today. The biblical doctrine of Christ continues to be challenged. Those seeking the biblical and theological tools to combat the contemporary restatement of ancient heresies and contemporary denials of orthodoxy would do well to revisit the works of Cyril of Alexandria.