Not all Muslims are keen on the comparison either. Ingrid Mattson, professor of Islamic studies and Christian-Muslim relations at Hartford Seminary in Hartford, Conn., says "[If Christians assert] God is Trinitarian and that God includes Jesus, then Muslims do not in fact believe in that God." Islam portrays Allah, the Arabic name for God, as a single whole who cannot be divided into multiple parts.
How should a Catholic respond to this?
Well, we can begin by pointing out that the Muslims are right: God cannot be divided into parts. In fact, the doctrine of the Trinity emphatically denies that God has any parts or that He can be divided into parts. If divinity could be separated or divided, there would be three gods, not one. The idea that the Three Persons are “parts” of God, or are separable, or capable of being divided is, therefore, a Christian heresy. Rather, the three Persons of the Trinity can be distinguished only by the relations within the Godhead. In short, the divine Persons can be distinguished, but not divided or separated.
But this begs the question. It is most certainly the case that the Muslims do not accept the idea that the Godhead contains three divine Persons. It is likewise the case that they deny Christ’s divinity. Doesn’t that mean they worship a different God?
We have to be careful here. The Muslims are not alone in rejecting those two propositions: the Jews reject them as well. If we want to use this rejection to charge that Muslims worship a different god, then we’re going to have to lay the same charge at the door of the Jews as well. Yet no one has ever argued that Christians and Jews worship different gods.
There are two reasons for this. First, Christians understand that Christianity is the fulfillment of Judaism. Jews are our elder brothers in the Faith. That means we must be worshipping the same God. If Jews and Christians aren’t worshipping the same God, then Christianity has had a serious misunderstanding about Judeo-Christian relations since at least the time of Paul’s letter to the Romans.
Second, both St. Paul and the Catechism of the Catholic Church insist that the Second Coming of Christ, which Christmas anticipates, “is suspended at every moment of history until his recognition by ‘all Israel’, for ‘a hardening has come upon part of Israel’ in their ‘unbelief’ toward Jesus.” (CCC #674). That means that Christ’s second coming is dependent on the fact that Jews and Christians worship the same God. Thus, the rejection of Trinity and Christ's divinity doesn’t necessarily mean their object of worship is different than ours. If that is true for the Jews, than it would likewise be true for the Muslims.
But let's cut to the heart of the matter and stop mincing words. There is only one God. Jews, Christians and Moslems are all monotheists. This has certain implications that cannot be avoided in casual conversation. When one monotheist charges that another monotheist “worships a different God”, the first is saying, in a pleasant way, that the second worships demons. That’s a fairly significant charge, and a good Christian would want to make sure of his facts before making it.
The Second Vatican Council, moving under the inspiration of the Holy Spirit, recognized that this charge wouldn’t stick. The fathers of the Council wrote:
“[The Muslims] adore the one God, living and subsisting in Himself, merciful and all-powerful, the Creator of heaven and earth (5), who has spoken to men; they take pains to submit wholeheartedly to even His inscrutable decrees, just as Abraham, with whom the faith of Islam takes great pleasure in linking itself, submitted to God. Though they do not acknowledge Jesus as God, they revere Him as a prophet. They also honor Mary, His virgin mother; at times they even call on her with devotion. In addition, they await the day of judgement when God will render their deserts to all those who have been raised up from the dead. Finally, they value the moral life and worship God especially through prayer, almsgiving and fasting. “
On Non-Christian Religions, #3
So, what exactly is the relationship between the three faiths? In order to understand the problem, we have to recognize a few simple truths about divine revelation. There are two types of divine revelation: natural and supernatural.
Natural revelation definitely teaches us things about God. “The heavens are telling the glory of God” says David, and every pagan knows it. Only a very small percentage of people are so intellectually and spiritually impoverished that they can look at the natural world and not see God’s handiworks.
All of creation was made by, through and for Christ, so all of creation tells us about Him. This is why pagan religions exist - pagans understand that God exists and that He rewards those who seek Him (Heb 11:6). This is, incidentally, the minimum necessary for salvation, which is why even pagans can be saved. The natural law, written on their hearts, might be enough to save them on the Last Day (Rom 2:14-16).
Still, though God reveals Himself through nature, not much of His revelation comes through clearly by that route. God is Three Persons, Persons are distinguished only by relations, and nature does not contain any visible created persons besides us human beings, so the medium of nature simply isn’t conducive to revealing much about God. That’s why pagans tend to be so wildly divergent in their faiths. They don’t have much to work with, and they have to make up the rest as they go along.
This is also why God revealed Himself to Abraham and the prophets directly. Persons have relationships; persons can reveal themselves much more fully through relationships than they can through inanimate objects (present essay excepted, of course).
Thus, when God revealed Himself directly to Abraham, He could make Himself much better known. But even so, He could not reveal Himself entirely. Even Moses, who alone was humble enough to see God face to face and talk with Him as a man talks with a man, even he had to veil his face after each encounter, because his encounter with divinity caused his face to glow with the divine light. Apart from John the Baptist, he was the best-prepared Old Testament prophet, and it still wasn't enough.
It is only through Christ that God fully reveals Himself, and even then, the full revelation comes only through the Paschal Mystery - the Passion, Death, Resurrection and Ascension. In short, even Christianity didn’t have a real shot at absorbing the full revelation of divinity until about the beginning of Acts 2.
Now, no matter what the source of the supernatural visions Mohammed had, he clearly obtained at least some accurate information about God. He knew God is both just and merciful, that His mercy triumphs over His justice, that prayer and almsgiving are powerful before the throne of God, and that Mary is to be honored. These are not trivial things, and in these details, they know is as much or more than even today's Jews know. Certainly, if every Catholic paid the same level of attention to prayer and almsgiving that many Muslims do, the sacramental graces God showers on us would be much more visibly evident, and the amount of schism and heresy in the world would be correspondingly reduced.
Just as clearly, however, Mohammed was not given the full revelation of God. How could he have been? He doesn’t even pretend to assert that he had direct conversations with God, as Abraham and Moses did, or as any number of the inhabitants of first century Jerusalem did. He says he just talked to an angel. As a result, his understanding of God’s covenant with man is radically impoverished compared to that of Abraham or Moses or any of their descendants. It is certainly nothing like as full as St. Peter’s or St. Paul’s knowledge of the divine covenant.
In this, the Muslims are much worse off than the Jews or the Baptists. Muslims understand that a covenant exists, and they understand many of God’s divine attributes, though not all of them, as they themselves readily admit. So, we may summarize by saying that, like anyone without an adult understanding of Catholic Faith, the Muslims have a partial revelation of God. It is a much more sophisticated understanding than 99% of the faiths that have ever existed, though it is not as sophisticated as the Jewish understanding, which in turn, is not as sophisticated as a non-denominational Christian’s understanding, which, in turn, is not as sophisticated as Catholic understanding.
This does not mean Christian relationships with Islam are likely to be all tea and crumpets. Indeed, converting followers of Islam to Christianity has long been noted as one of the most difficult feats to accomplish - even St. Francis of Assisi made essentially no headway in this area. If nothing else, that fact should give both Catholics and American presidents pause.