This must not be taken for a rigid piece of mutually exclusive division, for the edges of character are not cut exactly sharp, as words are.  Especially when any type is intense, it seems to meet and touch its opposite.  Just as Voltaire’s piercing activity and soundness of intelligence made him one of the humanest of men, so Rousseau’s emotional susceptibility endowed him with the gift of a vision that carried far into the social depths.  It was a very early criticism on the pair, that Voltaire wrote on more subjects, but that Rousseau was the more profound.  In truth one was hardly much more profound than the other.  Rousseau had the sonorousness of speech which popular confusion of thought is apt to identify with depth.  And he had seriousness.  If profundity means the quality of seeing to the heart of subjects, Rousseau had in a general way rather less of it than the shrewd-witted crusher of the Infamous.  What the distinction really amounts to is that Rousseau had a strong feeling for certain very important aspects of human life, which Voltaire thought very little about, or never thought about at all, and that while Voltaire was concerned with poetry, history, literature, and the more ridiculous parts of the religious superstition of his time, Rousseau thought about social justice and duty and God and the spiritual consciousness of men, with a certain attempt at thoroughness and system.  As for the substance of his thinking, as we have already seen in the Discourses, and shall soon have an opportunity of seeing still more clearly, it was often as thin and hollow as if he had belonged to the company of the epigrammatical, who, after all, have far less of a monopoly of shallow thinking than is often supposed.  The prime merit of Rousseau, in comparing him with the brilliant chief of the rationalistic school of the time, is his reverence; reverence for moral worth in however obscure intellectual company, for the dignity of human character and the loftiness of duty, for some of those cravings of the human mind after the divine and incommensurable, which may indeed often be content with solutions proved by long time and slow experience to be inadequate, but which are closely bound up with the highest elements of nobleness of soul.

It was this spiritual part of him which made Rousseau a third great power in the century, between the Encyclopaedic party and the Church.  He recognised a something in men, which the Encyclopaedists treated as a chimera imposed on the imagination by theologians and others for their own purposes.  And he recognised this in a way which did not offend the rational feeling of the times, as the Catholic dogmas offended it.  In a word he was religious.  In being so, he separated himself from Voltaire and his school, who did passably well without religion.  Again, he was a puritan.  In being this, he was cut off from the intellectually and morally unreformed church, which was then the organ of religion in France.  Nor is this all.