St. Cyril is not an easy read—it’s both “technical and philosophically demanding” (McGuckin 32). Still, the effort is worth the struggle for this reason:

To this day Cyril of Alexandria’s theology represents a definitive theological vision for Eastern Christianity’s understanding of Christ, and the mystery of redemptive deification which the incarnation has effected. (McGuckin 16)

In On the Unity of Christ, Cyril attempts to explain a deep mystery: how the divine and human are united in Christ. He approaches the mystery through metaphor. For example, similar to the way that the soul and body are united in a human being, the divine and human are united in Christ. Jesus is one person with two natures, yet these natures are inseparable.

Cyril emphasizes this point with the doctrine called the “Communication of Idioms.” This doctrine emphasizes that the properties of Christ’s two natures are predicated of one person. Cyril’s prose underscores this point: “God wept. God died. God sat upon the Virgin’s lap and suckled” (McGuckin 45).

I also should mention that the way Cyril berates his opponents borders on the comical. (I wouldn’t want to debate him!)

My friend, this would be blasphemy, and a proof of complete madness, but doubtless it would evidently suit those who do not know how to conceive of the matter properly. (106)

It is rather the invention of a weak and feeble spirit that loves novelty and has no perception of the depth of the mystery. (88)

What a servile mentality from a crazed brain that knows how to do nothing else but gabble. (96)

Translator John Anthony McGuckin also wrote a short introduction which gives the novice reader the background required to navigate Cyril’s work. In the end, it’s difficult to overstate Cyril’s significance for Christology. On the Unity of Christ is a theological, historical, and profoundly devotional resource all rolled into one.

Cyril of Alexandria. On the Unity of Christ. Popular Patristics Series 13. Translated by John Anthony McGuckin. Crestwood: St. Vladimir’s Seminary Press, 1995.