In this letter, Frederick talks of his own faith being “lukewarm”, and cites that as the reason why he is able to tolerate the faiths of all others. He also discusses and expands upon his belief that “superstition is a weakness of the human spirit”.

Marie-Anne de Vichy-Chamrond, marquise Du Deffand begins the letter by stating that she has neither Voltaire’s erudition, nor his clarity, but that her opinions are nevertheless in line with his. She then discusses shared public opinions, and states that if common prejudices were taken from people, they would have nothing left. The Marquise then turns to the question of faith, and states that faith is firmly believing in what you do not understand. She notes that for Voltaire the search for truth is a universal medicine, as it is for her, but that they differ in that Voltaire believes he has found it and she believes it cannot be found. Speaking of modern philosophers, the Marquise remarks that they have never been less philosophical or tolerant men who would crush all who do not bow before them. She concludes by turning to her correspondence with Voltaire, saying that his letters honour her infinitely but that she does not have the vanity to make them a trophy. She notes that she had once read a letter, which was then memorised and printed without her consent and so now keeps her letters from Voltaire private. She additionally remarks on the letter Voltaire sent to the president, which she says he was very happy with.