In the year 610 A.D. a man named Muhammad began publicly preaching supposed revelations received from the Angel Gabriel, sparking a movement we know today as Islam. However, historical attitudes and beliefs about the religion are not the same as we know them today. You might be surprised to learn that Medieval Christendom actually condemned Islam as a Christian heresy, a thought still surviving today.
“Many false prophets will arise and deceive many; and because of the increase of evildoing, the love of many will grow cold. … they will perform signs and wonders so great as to deceive, if that were possible, even the elect.” – Matthew 24:11-12,24
During the Early Middle Ages following Islam’s proliferation, Christendom largely viewed Islam as a Christian heresy and Muhammad as a false prophet. By the end of the Late Middle Ages, consensus had Islam grouped with paganism, and viewed Muhammad as inspired by Satan. Public opinion only shifted slightly after the Islamic empires ceased to be an acute military threat to Europe.
It is worth noting that Muhammad’s uncle was an Assyrian Christian monk by the name of Sergius who held heretical views including elements of Arianism, Nestorianism, and possibly Gnostic Nasorean. It was from this relative that Muhammad likely was exposed to the Old and New Testament.
The earliest proponent of this position of Islam as a Christian heresy was Saint John Damascene, a man from an epicenter of Islamic expansion in Damascus who was witness to how Islam was molding and adapting itself in its nascent form. This is evidenced in his writings where he quotes a surah that is not generally present in today’s extant Quran.
In his dogmatic work Fountain of Knowledge, Saint John Damascene devotes a portion of the writing to a section titled Concerning Heresy. While a majority of its 101 chapters addresses various heresies succinctly in a few short lines, the final chapter is comprised of many paragraphs devoted to the “Heresy of the Ishmaelites,” the first Christian apologetic refutation of Islam.
In this cornerstone work of Christian apologetics on Islam, Saint John Damascene is first to call Muhammad a “false prophet” and the “Antichrist,” proclaiming he devised his own heresy.
“From that time to the present a false prophet named Mohammed has appeared in their midst. This man, after having chanced upon the Old and New Testaments and likewise, it seems, having conversed with an Arian monk, devised his own heresy. Then, having insinuated himself into the good graces of the people by a show of seeming piety, he gave out that a certain book had been sent down to him from heaven. He had set down some ridiculous compositions in this book of his and he gave it to them as an object of veneration.” – Saint John Damascene, Heresy of the Ishmaelites
Taking a historical approach, Muhammad drew on second-hand Biblical accounts from some of the Christians around him in Arabia. However, these Christians were unorthodox and would be considered gnostic today. As Bible translations were often rare and poor, and because a majority of Arabian gnostic Christians didn’t recognize the Bible as Holy Scripture, Islam has its roots in Biblical misunderstandings and thus was, and still is by some, considered a Christian heresy.
Saint Thomas Aquinas in Summa Contra Gentiles noted that Mohammed drew much of his thought from altered stories and teachings from the Old and New Testaments and subsequently forbade his followers to read them.
“Lastly, no divine oracles of prophets in a previous age bore witness to him; rather did he corrupt almost all the teaching of the Old and New Testaments by a narrative replete with fables, as one may see by a perusal of his law. Hence by a cunning device, he did not commit [forbade] the reading of the Old and New Testament books to his followers, lest he should thereby be convicted of falsehood.”
In his book The Great Christian Heresies, Hilaire Belloc predicted the future rise of Islam. He also identifies the religion as a Christian heresy. Belloc states Islam began as a perversion of Christian belief, saying:
“It began as a heresy, not as a new religion….It was a perversion of the Christian religion…an adaptation and a misuse of the Christian thing.”
He calls Muhammad a heresiarch that while not a man of Catholic birth, taught heretical doctrine drawing from Catholicism.
“The chief heresiarch, Mohammed himself, was not, like most heresiarchs, a man of Catholic birth, and doctrine to begin with. He sprang from pagans. But that which he taught was in the main Catholic doctrine, oversimplified. It was the great Catholic world – on the frontiers of which he lived, whose influence was all around him and whose territories he had known by travel-which inspired his convictions.”
He evidences this by drawing the comparison between Islamic and Catholic belief, and pointing out where Islam perverses the belief to a heresy.
“Thus the very foundation of his teaching was that prime Catholic doctrine, the unity and omnipotence of God. But the central point where his new heresy struck home with a mortal blow against Catholic tradition was a full denial of the Incarnation. He taught that our Lord was the greatest of all the prophets, but still only a prophet; a man like other men. He eliminated the Trinity altogether.”
Finally, he explains how Islam is founded on simplification of true Catholic doctrines, and this simplification produced a Christian heresy.
“In other words, he, like so many lesser heresiarchs, founded his heresy on simplification…Simplicity was the note of the whole affair; and since all heresies draw their strength from some true doctrine, Mohammedanism drew its strength from the true Catholic doctrines which it retained.”