In this post I want to present an argument more from the pluralist perspective, one which I do not necessarily agree with but which is intriguing. It presumes the fact that God does work outside the visible bounds of one religion, and that He reveals Himself - whether through natural or supernatural means, it does not matter - to all men. It is given by Ibn al'Arabi, in Chapter 48 of al-Futuhat al-makkiyya, and translated by William Chittick, in Imaginal Worlds: Ibn al'Arabi and the Problem of Religious Diversity (Albany: State University of New York, 1994), pp. 158-160.
The revealed religions are diverse only because of the diversity of the divine relationships.
[A Christian must interpose that the only religions that are truly revealed in the fullest sense are Christianity and Judaism - but various orthodox theologians, such as Fr. Roch Kereszty in the journal Communio, have tried to explain how the Providential role of God has lead people in other religions through a "revelation to the heart" (my phrase).]
If the divine relationship demanded that a particular thing be lawful in the revealed law, ofr if the relationship demanded that something be forbidden, then divine rulings could not change, but it is established that divine rulings do change. And if divine rulings do change, then God's words would be incorrect: To every one of you [messengers] We have appointed a right way and a revealed law [surah 5:48]. [While I do not accept that the Qur'an as a whole is the revealed Word of God, this saying does seem to be true, and therefore the fruit of the Holy Spirit. God has left nobody without prophets and revelation - this is the Catholic dogma of the "natural law".] But every community does in fact have a right way and a revealed law brought to it by its prophet and messenger. So abrogation [of rulings] does take place.
We know for certain that God's relationship to Muhammed in what He revealed to him as religion is different from His relationship to any other prophet. Were this not so and were the relationship one in every respect - that is, the relationship that demands revelation of the specific law - then the revealed religions would be one in every respect. [One may question how much Muhammed - who seems to have started at genuinely seeking God, but corrupted into impurity by carnal attachments - understood of the workings of the Holy Spirit in his heart. But it is true that God related to him differently than He related to Moses, to St. John the Baptist, to Hermes Trismegistus - regarded as a prophet by the Church Fathers - and to the Roman sybil.]
If you ask: Why then are the divine relationships diverse? We will reply,
The divine relationships are diverse only because of the diversity of the states.
One person has the state of illness. He calls out, "O Cure-giver, O Healer!" Another is hungry and calls out, "O Provider!" Still another is drowning and calls out, "O Helper!" Hence the relationships are diverse because of the diversity of the states. [Yet Christianity is universal because we are all sinners - "all have sinned, and fallen short of the glory of God.] This is indicated by God's words, Each day He is upon some task... We shall attend to you at leisure, O mankind and jinn! [surah 55:29-31] It is also indicated by the Prophet's words while describing his Lord with the scales in His hand: "He lets down and lifts up." Because of the state of the Scales, God is called "Uplifter" and "Downletter". In the same way these various relationships become manifest in the diversity of the states of the creatures.
The states are diverse only because of the diversity of the times.
The cause of the diverse states of the creatures is the diverse times in which they dwell. Their state in the time of spring differs from their state in the time of summer, their state in the time of summer differs from their state in the time of autumn, their state in the time of autumn differs from their state in the time of winter, their state in teh time of winter differs from their state in the time of spring.
One of those who is learned in the way in which the times act upon natural bodies says that you should expose yourself to the air in the time of spring, because it does to your bodies what it does to your trees. [Not quite, but biology was in a rather primitive state back then!] And you should protect yourselves from the air of winter, because it also does to your bodies what it does to your trees. [That indeed it does - it freezes you!] And God has stated explicitly that we are among the growing things of the earth, for He says, God has made you grow out of the earth as growing things [surah 71:17]...
The times are diverse only because of the diversity of the movements.
I mean by movements the movements of the celestial spheres, for these movements give rise to night and day and delineate the years, months, and seasons. All this is what is known as "the times". [He's getting dangerously close to astrology here, and his argument's rather weak. How does the change in seasons justify different divine revelations for different tribes and peoples?]
The movements are diverse only because of the diversity of the attentiveness.
I mean by attentiveness God's turning His attention toward the movements to bring them into existence. [This is the philosophical doctrine of occasionalism, rejected by Christianity since it denies the subsistent existence and order of the universe and natural laws.] God says, Our only speech to a thing, when We desire it, [is to say to it "Be!" and it is] [surah 16:40]. If the attentiveness toward the movements were single, the movements would not become diverse, but they are diverse. This proves that the attentiveness that moves the moon in its sphere is different from that which moves the sun in its sphere or those which move the other planets and spheres. Were this not the case, the speed or slowness of all of them would be the same. God says, Each of them floats in a sphere [surah 21:33] [Unfortunately they fall in ellipses - astronomy was also in a primitive stage, and allegedly there are Muslims to this day who will reject modern astronomy because the Qur'an revealed that there are spherical orbits.] Each movement has a divine attentiveness, that is, a specific divine connection to it in respect of the fact that He is the Desiring.
The attentivenesses are diverse only because of the diversity of the goals.
[This is flatly wrong - teleological physics.] If the goal of the attentiveness that causes the moon's movement were the same as the goal of that which causes the sun's movement, no effect would become distinct from any other effect. But the effects are diverse, without doubt. Hence the attentivenesses are diverse because of the difference in goals. Thus God's attentiveness with good pleasure toward Zayd is different from His attentiveness with wrath toward 'Amr, for His goal is to chastise 'Amr and to give bliss to Zayd. So the goals are diverse. [Perhaps one can salvage this by pointing out that all that happens in natural processes happens according to divine providence - Providence gave the Earth the mass and orbit that it did, without detriment to any scientific explanation. However, since earlier "the times" were linked with the heavenly bodies, the chain of reasoning is broekn when we apply these "goals" to earthly people, unless and only unless we accept the pseudoscience of astrology.]
The goals are diverse only because of the diversity of the self-disclosures.
Were God's self-disclosures one in every respect, He could have no more than a single goal. But the diversity of the goals has been established, so every specific goal must have a specific self-disclosure that is different from every other self-disclosure. [Are we talking about the heavenly bodies as theophanies, the self-disclosure of God in the heavens, or on earth? Without astrology to link the two, the argument is broken.] For the divine Vastness demands that nothing be repeated in existence. [Why?] It is this fact upon which a group of the Sufis depend, even though The people are in confusion as to a new creation [surah 50:15]. Shaykh Abu Talib al-Makki, author of Heart's Food, and other men of God have said, "God never discloses Himself in a single form to two individuals, nor in a single form twice." That is why effects are diverse in the cosmos. [Yet there is much homogeneity.] These have been alluded to as "good pleasure" and "wrath" [yes, all human souls are unique and individual, but we have commonalities and God sometimes does repeat Himself, calling us to repentance over and over again - though the parable of Dives and Lazarus provides an example of God refusing to repeat Himself].
The self-disclosures are diverse only because of the diversity of the revealed religions.
[Certainly not if we are talking about God's self-disclosure in "the times" and heavenly movements, which have nothing to do with religions and were around for 13.74 billion years before the first religion was.] Each revealed religion is a path that takes to God, and these paths are diverse. Hence the self-disclosures must be diverse, just as divien gifts are diverse. Do you not see what happens when He discloses Himself to this community at the resurrection, while within it are hypocrites? Moreover, people's views of the revealed law are diverse. Each possessor of independent judgment [mujtahid] has his own specific law that is a path to God. [Some paths may not lead to God, however, and He has revealed to us The Way - as Christianity was called in the Apostolic era - in which He wants us to take, the narrow way or royal way as it is called.] That is why the schools of law are diverse, even though each is a revealed law, within a single revealed religion. [Example where al'Arabi's point is true: the different rites of the Catholic Church.] And God has established this for us on the tongue of His messenger.
So the self-disclosures are diverse, without doubt. Each group has believed something concerning God. If God discloses Himself to them in other than that something, they will deny Him. But when He discloses Himself in the mark that they have established for God in themselves, they will acknowledge Him. Thus, for example, when God discloses Himself to the Ash'arite in the form of hte belief of his opponent, whose knotting concerning God is opposed to his, or when He manfiests Himself to his opponent inf the form of the Ash'arite's belief, each of hte two groups will deny Him. And so it is with all groups.
Then, when God discloses Himself to each group in keeping with the form of their belief concerning Him - and that is the "mark" mentioned by Muslim in his Sahih, quoting from the Prophet - then they will akcnowledge that He is their Lord. But He is He, none other than He, so the self-disclosures are diverse because of the diversity of the revealed religions.
As for our words, "The revealed religions are diverse only because of the diversity of divine relationships," that has already been discussed. Thus the circle is closed. [It seems that this deliberately circular argument should have not included this step - the diversity of the self-disclosures is the fundamental starting point, and not really epistemologically justified by appeal to the plurality of religious forms. However, al'Arabi wanted a self-enclosed circle, and a circle he got. I leave it to the reader to judge the merits or unsoundness of his argument, considering my critiques.]