The equation of Decoud with Father Corbelan -- perhaps the most fanatic idealist in the book -- helps make the point that skepticism is essentially another form of dream-ideal: the ideal of non-ideals. That point is enhanced by the phrasing above, in which Decoud's pleasure in skepticism is portrayed as something he "imagines."

In the phrase "lead a man very far," we again find the dream-ideal described as an active agent that lures men on.