Lettres Provinciales arose from a theological dispute involving Antoine Arnauld, a leading figure associated with Port-Royal, whose views on grace and Jansenism were challenged at the Sorbonne. Pascal presents the early letters through an inquisitive narrator who encounters competing theologians and exposes what he regards as obscure terminology and disagreements beneath apparent doctrinal agreement. The conversational form allows complex disputes about grace, free will and religious authority to be presented through irony and satire.

The later letters concentrate on Jesuit moral theology, particularly casuistry and probabilism. Pascal cites Jesuit authors while arguing that some methods of moral reasoning permit actions that conflict with stricter Christian teaching. He also responds to objections from his opponents and defends his use of their writings. Across the series, theological argument is combined with satire, dialogue and close attention to language, making the work both an intervention in contemporary Catholic controversy and a significant example of French polemical prose.