In his book _Du Pape_, which Catholics consider a work of the first importance, he carries his reasoning on ecclesiastical matters to its logical conclusion.
This book was the outcome of the remorse he felt for having, at a trying moment, forgotten the reverence due to the head of the church. When, three years after the conclusion of the Concordat, the Pope went to Paris, at Napoleon's request, to anoint and crown him Emperor, Joseph de Maistre, the ardent royalist, was so incensed that in various letters to his court he used such language in writing of the Holy Father that his _Mémoires et correspondance diplomatique_ of these years were published by Cavour in 1858 with the view of depriving the papal power of a spiritual ally. In the course of a few years Napoleon and the Pope quarrelled, and when De Maistre saw the Pope insulted and ill-used by the Emperor, he repented his hasty words, and resolved to make ample reparation.
The fundamental idea of _Du Pape_ is that there is no human society without government, no government without sovereignty, and no sovereignty without infallibility. This attribute of infallibility is so indispensable that men are obliged to assume its existence even in secular societies (where it does not exist) on pain of seeing these societies dissolved. The church lays claim to no more than do the other authorities, although it has this immeasurable advantage over them, that its infallibility is not only taken for granted by man, but also guaranteed by God.
De Maistre writes: "A great and powerful nation has lately, before our own eyes, made the most strenuous efforts in the direction of liberty which the world has ever beheld. What has it gained by these? It has covered itself with ridicule and shame, and has ended by setting a Corsican gendarme on the throne of the kings of France." He shows how the Catholic religion necessarily forbids every kind of revolt, whereas Protestantism, which is a result of the sovereignty of the people, leaves the decision of everything to private feeling--a supposed species of moral instinct. "There is such accordance, such a strong family likeness, such interdependence between the papal and the kingly power that the former has never been shaken without the latter suffering too." As a proof of this he quotes the following utterance of Luther: "Princes are as a rule the greatest fools and the most arrant rogues on the face of the earth; nothing good can be expected from them; they are God's executioners, whom He employs to chastise us." He avers that Protestantism, which has no reverence for royalty, has no respect for marriage: "Had not Luther the audacity to write in his exposition of the book of Genesis (1525) that the example of the patriarchs leaves it an open question whether or not a man may have more than one wife, that the thing is neither sanctioned nor forbidden, and that he, for his part, will not take it upon him to decide one way or other?--edifying doctrine, of which practical application was soon made in the family of the Landgrave of Hesse-Cassel." (Luther gave his consent to this prince having two wives at the same time.)