Christianity and Islam: The First Meetings
Islam and Christianity have a long and storied history over the past 1400 years, marked by instances of fierce violence, misrepresentation, and misunderstanding. From Islam’s earliest years, relations between the two major faiths were complex. Was Islam a new religion, a sect of Christianity, or a new heresy? Early Byzantine Christians were among the first to interact with the new faith.
Muhammad lived during the early 7th century in the city of Mecca. By the time of his birth, the great Councils of Nicaea and Chalcedon had already solidified the doctrine of the Trinity and outlined orthodox Christology. Christianity had enjoyed a favored status throughout Europe and the Middle East for 300 years since the time of Constantine the Great. The Church had spread rapidly and had clearly defined itself against other faiths and heretical groups.
Around Muhammad’s birth, Christians, Jews, and local polytheistic cults were vying for influence on the Arabian peninsula . However, the Christians found in Mecca during Muhammad’s lifetime were most likely Nestorians , a heretical group who had been condemned at the Council of Ephesus 170 years earlier for drawing too sharp a distinction between Jesus’ divine and human natures. In Muhammad’s understanding of Nestorianism, they downplayed Christ’s divinity, which he approved of .
In Islam’s Scriptures, the Qur’an, Muhammad articulated a concept called the ahl al-dhimma, meaning “the people of protection” . Christians were included in this category. “The [Muslim] believers, the Jews, the Christians, and the Sabians-all those who believe in God and the Last Day and do good-will have their rewards with their Lord. No fear for them, nor will they grieve” . "You are sure to find that the closest in affection towards the believers are those who say, ‘We are Christians,’ for there are among them people devoted to learning and ascetics. These people are not given to arrogance, and when they listen to what has been sent down to the Messenger, you will see their eyes overflowing with tears because they recognize the Truth [in it]. They say, ‘Our Lord, we believe, so count us amongst the witnesses" .
During Muhammad’s lifetime, he sent letters to Christian communities in Muslim territories promising protection. An example of such a letter is on display at St. Catherine’s Monastery in Egypt. The letter, commonly known as the Ashtiname of Muhammad, declared the monastery will be given religious freedom and was sealed with Muhammad’s handprint . Such letters were significant as Islam conquered the Middle East at a steady pace, taking major cities such as Damascus and Jerusalem and overtaking the Persian Empire by 651 CE , less than a mere twenty years after Muhammad’s death. The conquest of Jerusalem in 638 CE was a defining event in future military and political encounters between the two faiths. Muslim Caliph Umar built a mosque over the ruins of the Jewish Temple’s old foundations. Years later, the same site would be dominated by the Dome of the Rock “to mark the victory of Muhammad’s revelation over Christianity, by creating a building which would be as impressive as anything that Christianity had put up” . The second reason for Muhammad’s letters of correction were statements in the Qur’an which encouraged killing unbelievers: “When the [four] forbidden months are over, wherever you encounter the idolaters, kill them, seize them, besiege them, wait for them at every lookout post” . Nestorian Patriarch Henanisho I of Mecca summarized his impression of Islam: “It is a power that was established by the sword and not a faith confirmed by divine miracles, like Christianity and like the old law of Moses” .
As the Middle East and, later on, Europe, braced themselves for the military threat of Islam, theologians found themselves grappling with the new teachings of Muhammad and the Qur’an. According to historian Jaroslav Pelikan, “The rise of Islam meant that the trinitarian monotheism defended by orthodoxy against Jews and dualists now faced a new challenge from the religion of the prophet. It was a challenge for which Christian theology was not well prepared” . Much of Christian history for the preceding centuries had been comprised of arguments over the Trinity and Christology, the great Councils dealing with those debates, and preceding interpretations and defenses of the Councils. Islam challenged the Church’s stance on both issues in a new form and with a highly effective military organization behind it.
Early Christian critiques were focused on the Qur’an itself. The Church claimed to have its own copy of the Qur’an at the Church of John the Baptist in Damascus . By the ninth century, a scholar named Nicetas had provided a point by point refutation of the Qur’an. Pelikan aptly summarizes the Byzantine Christian perception of the Qur’an:" Unlike the Old Testament and the New Testament, the Koran was filled with contradictions. Its style was ‘neither prophetic nor historical nor legislative nor theological,’ and yet Muslims claimed that it had come down from heaven. Even when it was acknowledged that the Koran contained ‘many true and clear statements about God and about our Lord Jesus Christ, things that we also confess,’ this was dismissed as insufficient" .
Disagreements between Christianity and Islam were centered on the Muslim confession, Shahadah: “There is no God but Allah and Muhammad is his prophet.” Islam was a strictly monotheistic tradition and, alongside Judaism before it, rejected the Christian doctrine of the Trinity. The Qur’an stated: “Those people who say that God is the third of three are defying [the truth]: there is only One God. If they do not stop what they are saying, a painful punishment will afflict those of them who persist” . Since the doctrine of the Trinity was formulated to protect the deity of Christ, Islam also rejected any notion of Christ’s divinity: “Those who say, ‘God is the Messiah, the son of Mary,’ are defying the truth” . “In God’s eyes Jesus is just like Adam: He created him from dust, said to him, ‘Be’, and he was” . Such statements could be volatile in the still tenuous orthodoxy of Chalcedon.
At first, as Islam conquered various territories, they did not articulate their new faith to conquered peoples and could be understood as fitting one of the heretical sects of Christianity. Historian Diarmaid MacCulloch states, “It might have been possible for Christians initially to regard these newcomers as a peculiar sort of Arian Christian sect, while Dyophysites would note with approval that they gave honour to the Virgin Mary without tolerating a cult of her” . An extreme approach to Islam identified it as “a summary of all the heresies that had arisen within the church” . "The Muslim view of God was attributed by the orthodox to Arian influence, while the doctrine of Christ was said to be Nestorian, apparently because it separated the man Jesus from the Logos. Manichaeism was the source for Muslim ideas about demons, and Origen was the source for the belief that the demons would be saved. Even ‘the heretical Donatists’ were blamed for Muslim error. On the basis of this ancestry, John of Damascus listed Islam in his catalog of Christian heresies. He also called it ‘forerunner of Antichrist,’ as had Maximus [the Confessor] before him and as later theologians did also….Such theologians were raising in acute form the issue of monotheism as in theory a common ground, but in practice the cardinal difference, between Islam and Christianity" 
The key difference in Islamic and Christian understandings of God was how both defined monotheism. For Islam, monotheism meant God is “altogether single,…without any partner” . On the other hand, Christians had “found itself obliged to hold its monotheism in some sort of tension with its no less central conviction that it was appropriate to speak of Jesus Christ as God” . Islam, with its strict definition of monotheism, demanded Christians explain why the doctrine of the Trinity did not imply tritheism . Christians spent more time defending the Trinity than Muslims did criticizing it, indicating this was a sensitive point for Christians in their interactions with Muslims . A letter by Emperor Leo III declared “anathema upon anyone who admits two or three divinities emanating from different origins” . These three persons (hypostases) “had one nature and were one [substance] (ousia)” . The mistake Muslims made in understanding the Trinity was in viewing the three persons as completely distinct, autonomous individuals. Christianity understood the three persons as being distinct persons with distinct roles, but they shared the same nature and substance.
Muslim misunderstandings of the Trinity inevitably led to misunderstandings of the role Mary played in Byzantine Christianity. Interestingly enough, Mary had been the divisive figure in the Nestorian controversy at the Council of Ephesus in 431. The Qur’an itself mistakenly includes Mary in the Trinity: “When God says, ‘Jesus, son of Mary, did you say to people, Take me and my mother as two gods alongside God”?’ he will say, ‘May You be exalted! I would never say what I had no right to say-if I had said any such thing you would have known it” . Christians, on the other hand, identified Mary as a “creature of God God and the handmaid of God” based on Luke 1:38 . She was honored as the Theotokos, Mother of God, but was not worshiped as a member of the Trinity. Honoring Mary and the saints with the use of icons was a sensitive subject in the Eastern Church during the eighth century as the iconoclastic policies of Emperor Leo III led to fierce debates and revolts over the use of icons. While dialoguing with Muslims, Eastern Christians emphasized the usefulness of icons for teaching purposes .
While Christians spent time defending the Trinity against Muslim attacks, they also took the offensive and criticized Islam’s own practice of monotheism. A mistranslation of the Qur’an described God as “all spherical” while a later revision said, “God is one, God is made of solid beaten metal”. Theologians used these translations to accuse Islam of identifying God with matter . St. John of Damascus also pointed out that Aphrodite had been worshiped at the Kaaba shrine and, in fact, her carving could still be seen until close to St. John’s own day . “The jinns and other intermediaries of Muslim belief were further proof that in Islam ‘the name “one God” is nothing but a screen’ for ‘an idolatrous adoration of the creature and a paganism’ that belied its protestations” . Actual Muslim worship did not fully conform to the strict monotheism Muslim theologians had used to criticize Christianity.
The other assertion of the Shahadah, “Muhammad is his prophet” was a further area of primary critique. Muslims had accused Christians of removing prophecies about Muhammad from the Gospels, including a statement from Christ: “I shall send you a prophet called Mohammad”. In this case, Christians demanded evidence of Islam’s claims, but there was no manuscript evidence to support Muslims' accusations . Christians bolstered their argument by pointing to passages regarding Christ’s humiliation. They reasoned that if Christians had wanted to tamper with the Gospels, they would have most wanted to remove such embarrassing statements, but they remained as evidence that Christians had not removed passages from the Gospels . Christians also cited differences in the Qur’an’s narratives of Moses and the Patriarchs from the Pentateuch itself and its differing portrayals of Jesus from the Gospels to show that Muslims denied the Old and New Testaments .
While Christians criticized Mohammad, the question remained: was Mohammad a prophet? St. John of Damascus defined a prophet as someone who “names Jesus as Lord” . Bartholomew of Edessa identified two marks of a prophet: he foretells the future and performs miracles. Muhammad had done neither . Two further marks were added, namely, “the adornment of his holy life and by his superior knowledge of divine truth” . Muhammad’s life was marked by violent warfare and polygamy, disqualifying him from the office of prophet. While not all of Muhammad’s Christian critics were themselves innocent of violence, none of them claimed to be a prophet.
A third and final key area of theological difference was the sovereignty of God. Both religions affirm the sovereignty of God. It could be included in a list of shared attributes between God the Father and Allah. Yet rather than argue that both are the same God or focusing on it as a point of agreement, Byzantine Christians found the Islamic portrayal of Allah’s sovereignty problematic. The Eastern Church had already encountered a similar debate with philosophical dualism and were prepared to use similar arguments.
Byzantine theologians believed Islam taught determinism . “O Allah, Master of all sovereignty! You give sovereignty to whomever You wish, and strip of sovereignty whomever You wish; You make mighty whomever You wish, and You abase whomever You wish; all good is in Your hand. Indeed You have power over all things” . Christians interpreted such passages from the Qur’an as teaching that God is the cause of both good and evil. Byzantine theologians accused Allah of being unjust by authoring evil . “The Christian alternative to such determinism was to assert the universal salvific will of God, but also to assert free will and responsibility in man” .
Byzantine theologians provided a precedent for treating Islam as a different faith from Christianity and critiquing its divergences from orthodox Christianity. Soon, Islam would not be the exclusive problem of the Eastern Church, but the Islamic armies would knock on the doors of Europe. Yet the upcoming era of Islam and Christian interactions would not be marked by dialogue and theological critiques, but the violence of the Crusades.
 MacCulloch, Diarmaid. Christianity: The First Three Thousand Years. New York: Penguin Books, 2011, p. 255.
 Poston, Larry,“Islam: Christian Contacts”, Muck, Terry C., Harold A. Netland, and Gerald R. McDermott, eds. Handbook of Religion a Christian Engagement with Traditions, Teachings, and Practices. Grand Rapids, MI: Baker Academic, 2014, p. 157.
 The Qur’an, Sura 2:62, translated by M. A. S. Abdel Haleem, Oxford World’s Classics, Oxford, 2016.
 Sura 5:82-83.
 “The Orthodox Christian Church's Patriarch Bartholomew”, published by CBS, August 8, 2010, https://www.youtube.com/watch?v=K6ZXxgjKk2o&frags=pl%2Cwn.
 González, Justo L. The Story of Christianity. Vol. 1. New York: HarperOne, 2010, p. 291.
 MacCulloch, p. 260
 Sura 9:5
 Quoted in MacCulloch, p. 256.
 Pelikan, Jaroslav Jan. The Spirit of Eastern Christendom (600-1700). Vol. 2. The Christian Tradition: A History of the Development of Doctrine. Chicago: University of Chicago Press, 1977, p. 227-228.
 Pelikan, p. 228
 Pelikan, p. 229
 Sura 5:73
 Sura 5:17
 Sura 3:59
 MacCulloch, p. 259
 Pelikan, p. 230
 Pelikan, p. 230-231.
 Pelikan, p. 231.
 Quoted in Pelikan, p. 232, emphasis added.
 Pelikan, p. 232.
 Sura 5:116
 Pelikan, p. 233
 Pelikan, p. 234
 Pelikan, p. 236.
 Pelikan, p. 237.
 Quoted in Pelikan, p. 237
 Pelikan, p. 237.
 Pelikan, p. 234
 Sura 3:26, translated by Mohammad Mahdi Gorjian
 Pelikan, p. 234.
 Pelikan, p. 235.