In order to truly understand the Christian faith, we must understand what it is not. Heresies have helped the Church clarify and define her teaching over the centuries. So to get a clearer picture of who Jesus is, it helps to identify certain Christological heresies and explain why they depart from the true Christian faith. There is no formula in Scripture for the Trinity. Rather, the doctrine of the Trinity was clarified more and more as the centuries went on, and as various errors appeared and were corrected with Scripture. The most basic definition of the Trinity is that God is one in nature, or essence, or being, but exists in three persons: the Father, the Son, and the Holy Spirit. The three persons fully share all that belongs to the divine nature – all the divine attributes (all-powerful, all-knowing, all-good) and the divine will, which are identical to the divine essence itself. The three persons do take on distinct roles in how they relate to us, but in eternity, the three persons are only distinct in relation to each other, as the Son is eternally generated by the Father and the Holy Spirit eternally proceeds from the Father and the Son. 

Arianism is the first major heresy that the Church addressed at an ecumenical council – the Council of Nicaea. Arianism is named after Arius, who stated that Jesus was of the divine substance, but wasn’t the eternal God Himself. Jesus was a creation of God the Father. His famous mantra was “there was a time when the Word was not.” The Church found this very problematic, because Jesus needs to be truly God in order to reconcile humanity to God. Jesus is truly human and truly God, which means He alone can bridge the gap between humans and God. Arius said that Jesus was of a similar substance (homoiousios) to the Father, but not of the same substance. (homoousios) Arius’s metaphor was that the Father is like the sun, and the Son is like the rays from the sun – made out of the same substance as the sun, but not the sun itself. Arianism was condemned as heresy for denying that Jesus is truly God, of one essence (consubstantial) with the Father. St. Athanasius was the chief defender of trinitarian orthodoxy against Arius and his followers, at one point being so outnumbered that his story is told as “Athanasius against the world.”

Apollinarianism is a heresy that was condemned at the second ecumenical council, the Council of Constantinople. It stated that Jesus had a human body, but a divine mind/soul. While Arianism denied that Jesus is truly divine, Apollinarianism denied that Jesus is truly human. Jesus needs to have a human soul in order to be truly human, or else He cannot redeem our souls. As Athanasius famously said, “that which has not been assumed can not be redeemed.” A lot of Christians assume that Jesus, even in His humanity, was omniscient from birth, and could have listed the entire periodic table of the elements or spoken Swahili as a newborn baby. However, this would make Jesus not truly human, because being human requires the limitations of the human nature. However, the Church must at the same time avoid the opposite error of Kenoticism, which states that Christ’s divinity was in any way lessened when He came into this world. Christ was truly divine from His conception to His ascension and for all eternity. However, Christ’s divine attributes, such as omniscience, were not always expressed through the human nature, meaning Jesus had to learn and grow, just like all other humans. 

Nestorianism was condemned at the Third Ecumenical Council, the council of Ephesus. Sadly, there are many Evangelicals today who either implicitly, or explicitly (in the case of people like John MacArthur) have a Nestorian Christology. Nestorius said that Mary is not the Mother of God, (Theotokos) but only the Mother of Christ, which is something that several Evangelical leaders say. The issue is not primarily about Mary herself, but that it indicates a larger issue in his Christology, because it denies the hypostatic union, even if it claims not to. The hypostatic union is the union of the divine and human natures in the one person of Christ. That means that the personal terms, Jesus, Christ, and God are interchangeable. So what we can say of Jesus, we can also say of God, because Jesus is God. If Mary is the mother of Jesus, she is the mother of God. If Jesus died on the cross, then God died on the cross. Not that the divine nature stopped existing on the cross, but that the divine nature was hypostatically united to the human nature that died, so it’s right to say that God died. It is right to call the blood of Jesus the blood of God, because Jesus is God, not because the divine nature has blood. However, Nestorians deny all three of these statements, leaving them with little more than a linguistic union between the divine and human natures of Christ, not a true personal union. A common conception of Nestorianism is the belief that Jesus is two persons. However, there is no proof that Nestorius himself taught this, nor is that primarily what he was excommunicated for. Christ being two persons is simply the logical conclusion of Nestorianism, if Mary gave birth to a person called Jesus Christ, but didn’t give birth to God. Almost nobody today, neither Evangelicals like John MacArthur nor the actual surviving Nestorian Churches known as the Assyrian Church of the East, would actually claim that Jesus is two persons. They would, however, separate Christ’s humanity and divinity by not translating “Mother of Jesus” to “Mother of God.” 

For every heresy, there is an equal and opposite reactionary heresy. In reaction to Nestorianism, there were those in the early Church who were Monophysites, meaning that they believed Jesus had only one nature. This was condemned as heresy by the Council of Chalcedon, because it would mean that Jesus is not truly human and truly divine, but some mixture of the two. Some forms of Monophysitism are more radical than others. There was Eutychianism, which essentially said the humanity of Jesus is absorbed by His divinity, completely denying the true humanity of Christ. Yet there is also Miaphysitism, the official position of the Oriental Orthodox Churches to this day, which says Jesus has one nature that is fully human and fully divine. It’s a heresy that’s modified enough to not quite be heretical, but it still causes unnecessary confusion in the Trinity by saying that Jesus doesn’t directly share His nature with the Father or with us, but rather has one nature that’s a union of two natures.

Another heresy that almost always gets forgotten in discussions of the Trinity and of Christology is Monothelitism, the belief that Jesus has one will as opposed to two. It’s probably unrecognized because it was condemned at the 6th ecumencial council, long after Chalcedon. While it’s certainly a much less grievous heresy than Arianism and even Nestorianism, it is still recognized as heresy. Dyothelitism, the orthodox position asserts that Jesus has a human will and a divine will – the same will as the Father and the Spirit. This is necessary, because Jesus needs to have a divine will to be truly God, and He must have a human will to be truly human. If Jesus did not assume a human will, then our human wills cannot be redeemed. 

The reason Monothelitism is the implicit belief of so many modern Christians is because our individualistic post-enlightenment culture assumes that a unique will is the definition of what a person is. So they assume that in the Trinity, will come with personhood, not nature. They assume what’s called Social Trinitarianism, that the Father, Son, and Holy Spirit each have their own will and that the person of Christ has one will. However, the classic view is that will comes with nature, so God has one divine will shared by the three persons of the Trinity, and Jesus Christ has two wills – a human will and a divine will. Monothelitism is also at the root of the Subordinationist heresy, the belief that the Son eternally submits to the Father. Jesus is indeed said to submit to the Father in scripture, but traditionally, that’s been seen as His human will submitting to the Father. His divine will can’t submit to the Father because it’s the same will as the Father’s will. However, if will comes with personhood rather than nature, then when Jesus is said to submit to the Father in scripture, it’s assumed to be an eternal subordination. 

A lot of Christians today do not see the importance of studying Church history. Conservative Evangelicals tend to say they just need the Bible and don’t need the help of Church history to interpret it. Liberal Christians tend to think the history of the Church is too filled with evil and oppression to be a reliable source of truth. However, trinitarian errors almost always emerge as a result ignoring Church history, because people tend to drift into one of several errors to try and make the Trinity more easy to understand than it is. Church history shows us which theological propositions have been proposed, which have been deemed unbiblical, and which have been shown to be true.