In these letters, Pascal humorously attacked casuistry, a popular rhetorical method used by theologists, and accused Jesuits of moral laxity. Being quickly forced underground while writing the Provincial Letters, Pascal pretended them to be the report of a Parisian to a friend in the provinces on the moral and theological issues then exciting the intellectual and religious circles in the capital. Pascal, combining the fervor of a convert with the wit and polish of a man of the world, reached a new level of style in French prose.
Aside from their religious influence, the Provincial Letters were popular as a literary work. Pascal's use of humor, mockery, and vicious satire in his arguments made the letters ripe for public consumption, and influenced the prose of later French writers like Voltaire and Jean-Jacques Rousseau. Brilliantly written by Pascal, the Provincial Letters were in fact the product of a collaborative work of theologians from Port-Royal, and most of the arguments used were already to be found in Arnauld's Théologie morale des Jésuites , which had led the Jesuit Nicolas Caussin to reply to the libel. The main source on Jesuit casuistry used by Pascal was Antonio Escobar's Summula casuum conscientiae (1627), several propositions of which would be later condemned by Pope Innocent XI.
Paradoxically, the Provincial Letters were both a success and a defeat: a defeat, on the political and theological level, and a success on the moral level . Thus, King Louis XIV ordered that the book be shredded and burnt in 1660. The final letter from Pascal, in 1657, had defied the Pope himself, provoking Alexander VII to condemn the letters. But that didn't stop most of educated France from reading them. And on the other hand, even Pope Alexander, while publicly opposing them, nonetheless was persuaded by Pascal's arguments. He condemned "laxism" in the church and ordered a revision of casuistical texts just a few years later (1665–66, and then 1679 ).
Structurally, the first three letters ridicule the dispute between the Thomists and the Jesuits on the nature of salvation, rather asserting a Jansenist understanding of salvation. Making allusion to the Congregatio de Auxiliis, the debate concerned the respective role of grace and free will, Molinists (i.e. Jesuits) claiming that an "efficacious grace" was not necessary to save man, but only a "sufficient grace" bestowed by God to all men, while Thomists claimed that the "sufficient grace," given to all men, had to be assisted by an "efficacious grace," bestowed only to the select few (in accordance also with Augustinism). Pascal thus highlighted, in the Second Letter, that neo-Thomists and Jesuits were using the same term, "sufficient grace", with two different senses, for political reasons.
The Fourth Letter deals with the question of "actual grace," the Jesuits claiming that sin could only be committed if people had knowledge of the evil inherent to the planned action. The Jesuit monk with whom Pascal was speaking quoted Le Moyne, a professor to the Sorbonne from 1642 to 1654 — Le Moyne's definition had already been used by Arnauld in the Apologie pour les saints Pères :
“1. On the one hand, God sheds abroad on the soul some measure of love, which gives it a bias toward the thing commanded; and on the other, a rebellious concupiscence solicits it in the opposite direction. 2. God inspires the soul with a knowledge of its own weakness. 3. God reveals the knowledge of the physician who can heal it. 4. God inspires it with a desire to be healed. 5. God inspires a desire to pray and solicit his assistance.”
“And unless all these things occur and pass through the soul,” added the (Jesuit) monk, “the action is not properly a sin, and cannot be imputed, as M. le Moine shows in the same place and in what follows.
Pascal replied, that this meant that all those whose "vices have got the better of their reason" and who indulge in "perpetual round of all sorts of pleasures", so long as they are ignorant of the immorality of their actions, were excused by this doctrine. While he argued, citing the Bible , that those who did believe in God but were deprived of knowledge of their evil actions (and thus deprived, for a moment, of the Jesuits' "actual grace") were still sinners.
Furthermore, Pascal ridiculized Etienne Bauny, author of a Somme des péchés qui se commettent en tous états (Paris, 1634 ), attempt to use Aristotle to justify this doctrine of sin (which could, according to Bauny, only be effective if man possessed the knowledge of the action). Bauny thus quoted the Nicomachean Ethics, III, 1, alleging that a voluntary action needed knowledge of what was good or evil in it. Pascal replied, also quoting Aristotle (he seemingly was the only one to use this argument in this debate ), that Aristotle spoke only of knowledge of the actual circumstances of the act, but not at all of the capacity to discriminate between good and evil — since Aristotle stated that one who was devoided of that capacity was not excused at all, but rather considered a vicious man.
The rest of the letters are mainly an attack on Jesuit casuistry. The Fifth letter, published in a hurry after a police search in Jansenist-friendly publishing houses, is particularly dedicated to criticisms against the Jesuits' doctrine of moral probabilism, according to which one could adopt a "probable opinion," that is, an opinion made plausible by the authority of a theologian, even if it was less probable than another opinion — especially concerning conducts to adopt, the nature of sins, etc. Pascal relied heavily on this witty attack, composed of quotes from various books written by Jesuit casuists, in particular by Antonio Escobar y Mendoza's Summula casuum conscientiae (1627), which had enjoyed a great success , and also Thomas Sanchez, Vincenzo Filliucci (Jesuit and penitentiary at St Peter's), Antonino Diana, Paul Laymann, Etienne Bauny, Louis Cellot, Valerius Reginaldus, Bernard Lamy (censored on 8 October 1649 by the Faculty of Leuven for his defense of homicide), etc.
In this letter, he evoked passing-by the Chinese Rites controversy which ended with the Jesuits' condemnation and the Congregatio de Propaganda Fide's decision to prohibit idolatry under any pretexts . He also alluded to the problem of the relations between Christian virtues and natural virtues, debated in particular during the first half of the 17th century. After Jean-Pierre Camus and Arnauld, Pascal attacked the Jesuit Antoine Sirmond, who had practically admitted the identity between natural virtues and Christian virtues .
Starting at Letter VI, dated 10 April 1656, Pascal gives a number of examples of Jesuit casuistry and of its "relaxed moral," citing abundant sources (a lot of whom came from Escobar). He illustrated casuistry by citing mostly Jesuitic texts allowing excuses to abstain from fasting (citing Vincenzo Filliucci's Moralium quaestionum de christianis officiis et casibus conscientiae... tomus, Lyon, 1622; often cited by Escobar); from giving to the poor (indirectly citing Gabriel Vasquez from Diana; for a monk temporarily defrocking himself to go to the brothel (citing an exact quote of Sanchez from Escobar, who was curving around Pius IV's Contra sollicitantes and Pius V's Contra clericos papal bulls, the latter directed against sodomite clergy )); in the Seventh Letter, propositions allowing homicides (even to the clergy) and duels as long as the intention is not directed for revenge; others permitting corruption of judges as long as it is not intended as corruption; others allowing usury or Mohatra contracts; casuistic propositions allowing robbery and stealing from one's master; others allowing lying through the use of rhetorical "mental reservation" (restrictio mentalis; for instance: saying, loudly "I swear that...", silenciously "I said that...", and loudly again the object of the pledge) and equivocations. A number of these scandalous propositions were later condemned by Pope Innocent XI.
In the Ninth Letter, the Jesuit explains to the narrator easy ways to enter Heaven, citing a book called “Paradise opened to Philagio, in a Hundred Devotions to the Mother of God, easily practised.” The Tenth Letter is dedicated to casuistic proceedals to lighten the ritual of confession and to the debate between the respective roles of attrition and contrition; the Jesuit character claiming that sole attrition combined with the sacrament of penance is sufficient for man's salvation, while the narrator insists on the necessity of contrition and of the love of God, citing extracts of the Bible often quoted by the Jansenists, the abbé de Saint-Cyran and Jansenius .
The Thirteenth and Fourteenth Letters criticize the Jesuits' legitimation of homicide. In the latter, Pascal abstains himself from discussing the most scandalous Jesuit propositions, legitiming tyrannicides and abortions. He quotes, among others, the Church's policies of penance for sinners guilty of willful murder officialized during the Synod of Ancyra (341).
In the Seventeeth Letter, Pascal took again the problem of the efficacious grace and of the "de facto vs de juris" debate concerning the inclusion, or not, of the 5 Propositions condemned by the Pope in the Cum Occasione papal bull, in Jansenius's work (see Formulary controversy for details). Port-Royal and Pascal argued that although the Pope had condemned these 5 Propositions as heretical, they were not to be found in Jansenius. Furthermore, they claimed that the Pope held authority only on matters of faith, and not on technical de facto matters. Thus, drawing on the Jesuits' argumentation itself, Pascal argued here that one could not be held heretical to believe that Jansenius' work did not include these 5 Propositions, and that the Papal condemnation only restricted itself to the heresy itself, not to the question of their inclusion in Jansenius' work. Thus, he recalled the Jesuit Cardinal Bellarmin's sentences concerning the authority of religious councils concerning matters of dogma versus de facto issues; he also recalled the debate between St Athanasius and St Basil concerning the interpretation of Dionysus of Alexandria, who was accused by Basil of Arianism and therefore convoked before the Pope Dionysius in 262; or the various contradictory papal interpretations given to the Scythian monks; as well as another debate concerning Pope Honorius I, who had been later anathemized by the Third Council of Constantinople, although Cardinal Bellarmin defended Honorius' orthodoxy, claiming that the condemned propositions were not to be found in Honorius.
They were first translated into Latin by Antoine Arnauld, and then into many other languages, including English in 1657 (Les Provinciales, or the Mystery of Jesuitisme, discovered in certain letters written upon occasion of the present differences at Sorbonne between the jansenists and the molinists, London, Royston, 1657) by the Anglican theologian Henry Hammond, while in 1684 a polyglot translation (in French, Latin, Spanish and Italian) was published by Balthasar Winfelt .
“You have not kept your word with me, sir,” said I. “This is not, properly speaking, to permit duelling; on the contrary, the casuist is so persuaded that this practice is forbidden that, in licensing the action in question, he carefully avoids calling it a duel.” (Letter VII)
“There is some sense in that,” I said; “for this is an excellent plan to induce sorcerers to aim at proficiency in their art, in the hope of making an honest livelihood, as you would say, by faithfully serving the public.”" (Letter VIII)