As usual, Schuon's perspective is far more universal than any single creed. He may or may not be correct, but one of his central principles is that each legitimate (God-given) revelation is an expression of universal metaphysics tailored to this or that cultural or ethnic group.
Thus the subtitle: Perspectives on Esoteric Ecumenism. For Schuon, the esoteric perspective is the only way to overcome certain inevitable incoherences and absurdities in religion -- not just in a religion, but between religions as well. As such, he is speaking of the "esoteric perspective" that transcends and unifies individual religions.
If such a thing exists. I think it is possible to take an intermediate position on the question. For example, rather than saying that only one religion is correct and all the others wrong; or that all religions are equally correct; or that all religions are equally wrong; we can say that this or that religion is a more or less adequate expression of certain truths embodied in religion as such.
Think of the analogy to music. We could say that "music as such" exists in the abstract. But in order to express musical truth or beauty, you need to "pick a path," so to speak, e.g., classical, jazz, blues, rock, whatever. Bach expressed the divine in one way, John Coltrane in another. We can't say that one or the other was wrong, even if we can affirm that one may have disclosed it more fully or adequately.
The book contains some previously unpublished letters, some of which touch on this question. For example, in one he writes that "A true metaphysician cannot unreservedly identify himself with a religious upaya [teaching or method] and take pleasure in it with a kind of nationalism, but obviously must identify with what is essential -- hence both universal and primordial..."
And yet, at the same time, Schuon always insisted that it was necessary to follow a particular religion -- just as you need a musical idiom to express music.
This is a tricky balance, for it seems as if one is trying to give oneself wholeheartedly to a religion even while holding a part of oneself in reserve, so to speak. He says, for example, that "theology tends to push" dogma "to the point of absurdity," but who could argue? Isn't this the problem of fundamentalism or literalism, which surely must alienate people who are not prepared to disable their God-given intelligence in order to embrace a "saving absurdity," so to speak.
In what Schuon calls the mundane "religious viewpoint" -- which you might say is a kind of worldly expression of the otherworldly -- there are certain "dogmatic elements" that are "unacceptable from the viewpoint of truth as such," even while "no doubt possessing a certain spiritually 'therapeutic' function." This cannot help sounding condescending, which would have once appealed to me very much.
Schuon suggests that "It is in the nature of theology to over-accentuate and exclude, and this is why no theology is intellectually perfect, though there are certainly degrees in this." I can't help agreeing with this, even though I also can't help feeling ambivalent about it.
In another letter, Schuon says he doesn't even like writing from the everyday religious perspective: "I would also just as gladly have preferred to spare myself having to deal with Muslim theology -- Lord knows how grating it can be -- but I had no choice since Sufism is situated parallel to this body of doctrine." More generally, "I am hardly enamored of exoterisms and would have preferred to deal only with pure metaphysics and the perennial religion..."
Regarding those latter two -- pure metaphysics and perennial religion -- Schuon was of the belief that the Vedanta was its most adequate expression. In another letter he writes that "we are of Christian origin, and our point of departure is the Vedanta," while being constrained to live in an essentially godless age.
Vedanta, of course, posits a radical monism. And yet, I don't see why it is intrinsically inconsistent with a trinitarianism that is an even "higher" or "deeper" expression of the same truth.
This is why one of my favorite cosmic pneumanauts is Swami Abhishiktananda, AKA the Catholic monk Henri Le Saux, who managed to reconcile the two in his own divided-but-united being.
He did so "through the medium of love, the axial Christian virtue.... The doctrine of the Trinity, understood in light of the advaita, 'reveals that Being is essentially a koinonia [fellowship] of love.' The inner mystery of non-duality 'flowers in communion and inter-subjectivity, revealing itself and coming to full expression in the spontaneous gift of the self to another.'"
"In 'the very depth' of the Upanishadic experience of identity, the Christian may discover 'a reciprocity and a communion of love which, far from contradicting... the unity and non-duality of being, is its very foundation and raison d'être.'"
Elsewhere he compares the Vedantic trinity of sat-chit-ananda to the Christian Trinity: "Being, sat, opens itself at its very source to give birth eternally to the Son..." (Very Eckhartian there.) It "is essentially 'being-with,' communion..., the free gift of the self and mutual communication of love."
Cit, i.e., consciousness or self-awareness "only comes to be when there is mutual giving and receiving, for the I only awakens to itself in a Thou."
Which I've only said about a billion times.
And ananda, the the ultimate felicity or beatitude, "is fulness and perfect fulfillment, only because it is the fruit of love, for being is love."
Ultimately "consciousness (cit) is identified with being (sat) in the infinite bliss (ananda) of the Spirit, who is... one in the Father and the Son, one in God and man, undivided [Sat-chit-ananda]."
"Thus, for Abhishiktananda, the Trinity 'resolves the antinomy of the One and the Many.'" "Christ's experience actually surpasses the Vedantic experience because it recognizes distinction... on its far side, as it were; for Jesus, God is both Other and not-Other."
Makes sense to me us three anyway.