But here his faith was larger than Voltaire's.

For while Voltaire referred the punishments and rewards to this life, the Abbe believed in the immortality of the soul, in heaven and hell.

He acknowledged that immortality could not be demonstrated, that it was only probable, but he clung to it firmly and even intolerantly.

It is clear from his writings that his affection for this doctrine was due to its utility, as an auxiliary to the magistrate and the tutor, and also to the consideration that Paradise would add to the total of human happiness.
But though his religion had more articles, he was as determined a foe of "superstition" as Voltaire, Diderot, and the rest.

He did not go so far as they in aggressive rationalism--he belonged to an older generation--but his principles were the same.
The Abbe de Saint-Pierre thus represents the transition from the earlier Cartesianism, which was occupied with purely intellectual problems, to the later thought of the eighteenth century, which concentrated itself on social problems.