Peter Leithart passes on Donald Fairbairn’ s explanation of the debate between Cyril of Alexandria on the one hand and Nestorius and Theodore on the other. If you’re interested in this subject, work through the whole post here. Here’s the first paragraph:
In his Grace and Christology in the Early Church (Oxford Early Christian Studies), Donald Fairbairn lays out some helpful distinctions that clarify what was at stake in the Nestorian controversy. He initially lays out a distinction between “composite” understandings of the unity of Christ and “synthetic” understandings: “By a synthetic union,I mean a union in which God the Logos added humanity to his own person, so that the one prosopon of Christ is the Logos himself. In this view of the incarnation, Christ is a synthesis of deity and humanity in the sense that he includes both elements, but he is not a composite because these two elements were not building blocks from which his person was constructed; his person already existed as the eternal Son. On the other hand, by a composite union, I mean either the combining of divine and human natures to create the prosopon of Christ, or the conjoining or uniting of two personal subjects (the Logos and the man) so that they can be called a single prosopon. In both of these views, the prosopon of the union comes into existence at the incarnation, and so thatprosopon is a genuine composite.” Theodore and Nestorius propose composite Christologies, while Cyril insists on a synthetic union.
Christologically, Jesus has two natures, and thus two distinct energies, but in the actual performance of any act, it is the single hupostasis at work, synthesizing both energies. The energies “interpenetrate,” Maximus [the Confessor] argues, and this interpenetration takes place “in the register of hupostasis.” Naturally diverse energies are evident “by virtue of the inexpressible union,” and thus “divine things are done humanly and human things divinely.”
Whom do the wind and waves obey? Who walks on the water? Who hungers in the wilderness and sweats blood in Gethsemane? Who dies on the cross? The answer is always the same: These are the acts of Jesus Christ, the only Son of God, always doing divine things humanly, and human things divinely.
UPDATE (3/6/12): Leithart posted again about this on Feb. 23, quoting Wheaton College’s George Kalantzis’ contrast between the Antiochenes, who constructed their Christology on the basis of “divine transcendence, immutability, and impassibility,” and Cyril, who stuck closer to the Scriptures without sacrificing those things.