This week's heresy is Nestorianism. As we progress through these Christological (i.e., having to do with the nature of Christ) heresies, we take a logical path, following the 3rd-5th century Church's path of discovery. This whole time, we're asking the same question: "Who is Jesus Christ, and how does that affect our salvation?"
With the Arian heresy, the Church struggled with the question of whether Christ was fully divine, and they concluded that in order for him to offer humanity any salvific benefit he must be. Then, the Church asked whether Christ was fully human (Docetism/Appolinarianism)--the logical outgrowth of the Arian debate. Concluding that Christ must truly be fully human, the Church articulated its belief that God didn't just take the form of a human but God actually became human, and that also was essential for salvation. This week, having established that Christ is both fully divine and fully human, we turn to the question of how those two natures become united in the Incarnation. And that was the question of Nestorius and his followers.
The debate began with the question of Mary--the one who gave birth to Jesus Christ. For centuries, the Church had understood her as Theotokos or "God-bearer," but Nestorius (and Theodore and others) took issue with that designation. How, they asked, could Mary have given birth to the divine? If in the Arian debate we established that Christ, as fully divine, is coeternal with the Father, how could Mary have borne God the Son? Instead, he suggested that Christ's two natures (fully divine & fully human) be united but also held distinctly separate, saying that Mary gave birth to the human nature ("Christotokos") but not the divine nature. As that theological conversation continued, the result was a Christ with very split natures. (Actually, Nestorius chose some poor language to describe the union, offering words that implied that Christ might have been two persons. Cyril of Alexandria latched on to this use of language and took Nestorius to the cleaners for it--even though that was likely a distortion of Nestorius' actual teaching.)
Convinced of his correctness, Nestorius, patriarch of Constantinople, called for an ecumenical council, and in 431 CE the Council of Ephesus was held. Unfortunately for Nestorius, Cyril's polemic against him was too strong, and Nestorius and his followers were anathematized. Mary was declared Theotokos, and the union of the divine and human natures in the person of Christ was declared to be ontological ("really real") rather than simply accidental ("just because").
Why bother with the Orthodox position? Are we really just worried about the BVM getting offended because her title changes? Not at all! This is a heresy that, like the others we've covered, focuses on salvation. If the human and divine natures were not fundamentally (ontologically) untied to each other, then the only way they hold together in the person of Christ is as a result (accident) of Christ's will. In other words, unless the natures are fully bound to each other, it's up to the Jesus, by the sheer power of his will and self-control, to hang on to both. If that were the case, the only way our human nature could be bound to God's divine nature (essential for salvation) is if our wills were as powerful as that of Jesus. But, of course, they aren't. We fail to align our will with that of God (a state called "sin") all the time. Only if in Christ the human and divine are fully united can we have our human nature fully united to the divine nature. And that's how salvation happens.
When our human nature is united to the divine (by virtue of our baptism into Christ's death and resurrection), something happens to our humanity. It changes. It is refined. It is purified by its union with the divine nature (which, by definition, cannot be changed or soiled by its union with our human nature). As a result, the Council of Ephesus affirmed that our salvation is accomplished in the Incarnation--when the human and divine are fully united.
Here's the PowerPoint slide show from this week's class. It explores this in more detail, including the place of scripture in the debate. Next week, we turn to Eutychianism--the next logical question about Christ's nature. In that class, we'll ask more about the nature of the union of Christ's two natures, exploring what happens to the two natures when they come together so fully.