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In 1932, Frank Hugh Foster penned an article entitled “Is Islam a Christian Heresy?” He set out to prove the affirmative by making his case by showing the affinities of Christianity and Islam. That same year, in the journal, The Moslem World, another author, D.S. Margoulith responded in the negative. Since this difference of opinion has existed since John of Damascus in his Heresy of the Ishmaelites alleged that Islam was a heresy in 749, while others objected, we must look a bit more closely at the question and some background thinking. Granted, moderns of the 21st century look at heresy as some kind of outdated and judgmental stance, but as we will show, this idea has consequences among Christian missionaries.

Heresy defined:

Roman Catholic Canon law defines heresy as “the obstinate post-baptismal denial of some truth which must be believed with divine and catholic faith”(canon 751, 1983 Code), while the all-knowing Wikipedia says it is “any belief or theory that is strongly at variance with established beliefs or customs.” From the Bible, one reads in Titus 3:10 that a ‘divisive person’ should be shunned after some warnings, which leads the New Bible Dictionary to define the term as someone who “stubbornly chooses to form or follow his own group” and from 2 Peter 2:1 as someone whose doctrinal errors include even a denial of Jesus as Master and Redeemer.

The leader of a heretical group is known as a heresiarch, and this was even a term applied to Martin Luther, as he was excommunicated by Pope Leo X.

Is Islam a heresy and is Muhammad a heresiarch?

When John of Damascus set out to prove that Muhammad was a heretic, he made comparisons with Arius, who was a Christian that denied the divinity of Christ. He saw parallels, between them, but as some observers have noted, he did not distinguish the fact that Arius claimed to be a Christian, whereas Muhammad never did. Thus, a Roman Catholics like Robert Caspar and Michael Fitzgerald would say that since Muhammad was never baptized, and never held to the tenents of the Christian faith, he could not by definition be termed a heretic, nor Islam a heresy. The phrase, however, was very popular in medieval times, and even today, to, as it were, tar and feather Islam.

What makes things a bit complicated, however, is that during the time of Muhammad, and in the period between the apostles and his time, there were multiple heretical sects, and men like Arius, who could rightly be called a heretic. Thus, it is probably more fair to say, that Islam rose, partially as a response to these groups. It would be unwise, however, to analyze Islam, only as a response to such, and not to treat it on its own right.

From the 2 Peter 2:1 text, we do see that a fundamental denial of Jesus as Master — implying his divinity, and Redeemer — implying his role as Savior, constitutes a heretical position with respect to Biblical truth. In this way, one could say that Islam is a heresy of sorts. Samuel Zwemer, the famous missionary to Muslims, would not go quite that far, but put it in other terms:

If the Gospel of Christ in its simplest form (which is also its deepest mystery) includes the Incarnation, the Atonement and the Resurrection, then the world of Islam certainly needs our message for it is news and offers good news to every Moslem. Islam is not a Christian sect or a Christian heresy. It is an eclipse of the Christ as revealed in the Gospel. It is an Arabian palimpsest superinscribed over the message of Jesus by another hand. Its categorical denial of the deity of Christ, of the crucifixion, of the finality of Jesus Christ as God's messenger and of His way of life through regeneration is evident from the Koran itself.   Samuel Zwemer, The Art of Listening to God, (1940), 162-163.

Mission problems with calling Islam a heresy:

When Frank Hugh Foster wrote his article in 1932 he spent a great deal of time trying to make Islamic doctrines sound very Christian. He was working under the assumption that Islam is not a non-Christian, or anti-Christian religion, but rather it was a quasi-Christian religion, which was encrusted with some barnacles of error, and which needed a thorough scrubbing.

For instance he lists ten, what he calls “great doctrines of Islam” including, "The divine remission of sins to believers" and "The change from unbelief to belief wrought by the overflowing grace of God."

And then goes on to say,

Now, here are the great doctrines of Christianity, found in no other religion, not all of them even in Judaism. They are, to be sure, very defective, and surrounded by great errors, and need the correcting and supplementing influence of a complete and pure form of Christianity. But Christian they are, both in fact and in origin! They constitute the very heart and substance of Islam, and they are also the very heart and substance of Christianity. And they are enough to justify our title, that Mohammedanism is an heretical Christianity.The reader, must pause. Foster, just argued that the essential doctrines of Islam are Christian. Imagine the ramifications of this suggestion.

1. Muslims are not seen as walking in the darkness of spiritual blindness, as per the Bible, but they are only in need of corrective lenses for their vision defect.

2. Muhammad was not a false prophet, as per the Bible, but actually someone who brought spiritual and saving truth.

3. Muslims should not be called to leave the darkness and come into the marvelous light of Christ, as per the Bible, but they already have the light of Christ, albeit a bit dim.

4. The language of conversion, of making an about face and turning from one’s religion, to embrace faith in Christ would not be required, as per the Bible, but they could just “stay where they are” — to take a verse out of context, as many have done.

5. Muslims could be seen as essentially Christian, or proto-Christians, who simply need a bit of coaching to remove the encrustations of some errors that have crept in.    

6. The Qur’an would not be seen as a text which is systemically anti the person and work of Christ, but as a collection of Christian doctrines in need of a bit of fine tuning.

Does this sound far-reaching, and only in the realm of theoretical possibility? Think again.

Consider these quotes from modern mission workers whose names I will keep anonymous:

“Islam is partly mistaken, but mostly full of half-completed truth and suppressed truth; it began to build the right kind of house but it veered off course and never completed it…. [They can call]… Muslims back to what truth can be found in the Qur’an and then on into a completed and full understanding of truth as found in the New Testament.” (2009)

  “I am suggesting that…[…] it is possible to re-read the Quran with the  hermeneutical key of the Old and New Testaments and develop an entirely new interpretative result.” (2006)

 "The late [….] (famous mission leader) saw early Islam as a contextualization of the biblical faith for those Arabs who rejected the alien and unbiblical character of Arabian Judaism and Christianity.”

What each of these authors is saying, is that Islam is a kind of distorted ‘Christian’ religion and that with some re-interpretation, it can be made Christian again. They are following Foster’s logic very closely. The problem with this view, is that they have Christianized Islam, and are determined to see it through Christian glasses. Here is a response of a Muslim who strongly resists this kind of alien reading into his religion: Sayid Hossein Nasr, editor of a new study Qur’an, and widely published, says the following,

If we accept the Qurʾanic version [of the crucifixion], the Christian version of Christ must be rejected. If we accept the Christian version, even the Judaic-Christian version, the Qurʾanic version cannot be accepted. Furthermore, to suggest that the Qurʾan had the wrong Christology makes absolutely impossible any dialogue with Islam... [...] when it comes to the question of the life of Christ, the historical life, on the level of fact it is either the Christian or the Islamic version that can be held.

In a word, Nasr leaves no room for a  Christianizing of a book which he sees as thoroughly Islamic and nothing else. Yet, Foster and the three authors mentioned, continue to propagate their ideas, as if they are useful. They are not.


We asked the question, “Is Islam a Christian heresy?” and by extension “Is Muhammad a heretic?” From a Christian standpoint, we saw that by definition this means someone who has been expelled from a Christian community, and who had previously held orthodox Christian beliefs, and then had departed from them in some or many areas. Based on these definitions, we concluded that it is not wise to call Islam a Christian heresy, and we must admit that this term has been used to castigate Islam, Muslims and Muhammad. We also must maintain that responses to heretical Christian teachings, do enter Islam. We also observed that taking the position that Islam is a Christian heresy, as Foster and a few authors have done, conveniently sets them up for a mission strategy that is alien to the overall teachings of the Bible. Does this mean that we have no love for Muslims? Actually, seeing them as the Bible sees them, means that we truly see them as they are, and constrained by the love of Christ, we are willing to leave our comfort zones to bring the Good News of the Gospel, which is only good, when set in contrast to the very bad state of humanity outside of Christ. Perhaps the words of George Fry, echoing those of Zwemer and written almost fifty years ago in 1969 — although potentially grating on modern politically correct ears — still have something to say in answer to the question we first posed:

From its inception, therefore, Islam has been Christianity’s most dangerous doctrinal challenge. It offers ‘another Christ’, ‘another gospel’, another way of salvation. With a peculiar Christology, a divergent revelation, and an alternative presentation of the prophetic succession, Islam holds up to the world an interpretation of holy history and the life of Christ radically different from that reported in the Scriptures. For this reason some of the medieval fathers regarded Islam as a Christian heresy. It was a doctrinal deviation similar to Arianism. Regardless of the merits of that position, the danger is obvious. Islam takes the principles, personalities, events, and promises of sacred history and revises and uses this familiar
material in a manner foreign to the spirit and letter of primitive Christianity. This new synthesis is presented to the world as the pristine revelation of God. It is precisely at this point that Islam becomes Christianity’s greatest theological challenge, for it is the oldest and most widespread surviving revision of the Gospel.

- George Fry, Christianity Today, (1969) page 4.

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