Islam was a movement; that is why it has ceased to move.  For a movement can only be a mood.  It may be a very necessary movement arising from a very noble mood, but sooner or later it must find its level in a larger philosophy, and be balanced against other things.  Islam was a reaction towards simplicity; it was a violent simplification, which turned out to be an over-simplification.  Stevenson has somewhere one of his perfectly picked phrases for an empty-minded man; that he has not one thought to rub against another while he waits for a train.  The Moslem had one thought, and that a most vital one; the greatness of God which levels all men.  But the Moslem had not one thought to rub against another, because he really had not another.  It is the friction of two spiritual things, of tradition and invention, or of substance and symbol, from which the mind takes fire.  The creeds condemned as complex have something like the secret of sex; they can breed thoughts.