Those who believe it their duty to deny the legitimacy of the Prophet of Islam on moral grounds forget that the only question to be answered is whether or not Mohammed was inspired by God, it being quite irrelevant whether or not he was comparable to Jesus or conformed to some established morality. When one remembers that it was God who allowed polygamy to the Hebrews and commanded Moses to have the population of Canaan put to the sword it is clear that the question of the morality of such conduct is in no way involved: what alone counts in every case is the fact of the Divine Will, the object of which is invariable, but the means or modes of which vary by reason of the Infinity of its Possibility and secondarily, because of the limitless diversity of contingencies. Christians readily blame the Prophet for actions such as the destruction of the tribe of the Qurayza, but they forget that any Prophet of Israel would have acted in a still sterner way than he, and they would do well to recall how Samuel, by the order of God, acted toward the Amalekites and their king. The case of the Qurayza is also like that of the Pharisees in that it provides an example of the “discernment of spirits” that takes place automatically, as it were, upon contact with a manifestation of the Light.
However neutral an individual may appear so long as he is placed in a chaotic or undifferentiated environment – such as, for example, the Near Eastern world at the time of Mohammed, or indeed any environment in which a religious readaptation is about to take place – and however attenuated or obscured the fundamental tendency of the individual may appear in an environment of spiritual indifference such as we have just described, this tendency will spontaneously be actualized when faced with the alternative presented upon contact with the Light: and this explains why it is that when the gates of Heaven are opened by the lightning flash of Revelation, the gates of Hell open too, just as in the sensory world a light projects a shadow.
If Mohammed had been a false prophet, there is no reason why Christ should not have spoken of him as he spoke of Antichrist; but if Mohammed is a true Prophet, the passages referring to the Paraclete must inevitably concern him – not exclusively but eminently – for it is inconceivable that Christ, when speaking of the future, should have passed over in silence a manifestation of such magnitude. The same reasoning excludes a priori the possibility that Christ, when making his predictions, intended to include Mohammed under the general denomination of”false prophets,” for in the history of our era Mohammed is in no sense a typical example among others of the same kind, but on the contrary, a unique and incomparable apparition. If he had been one of the false prophets announced by Christ he would have been followed by others, and there would exist in our day a multitude of false religions subsequent to Christ and comparable in importance and extension to Islam. The spirituality to be found within Islam from its origins up to our days is an incontestable fact, and “by their fruits ye shall know them.” Moreover, it will be recalled that the Prophet in his doctrine has testified to the second coming of Christ without attributing to himself any glory, unless it be that of being the last Prophet of the cycle; and history proves that he spoke the truth, no comparable manifestation having followed after him.
The Transcendent Unity of Religions by Frithjof Schuon, page 116-117.