The letter presents a plan for a citadel designed by Détalonde Morival, whose rapid progress in mathematics and engineering is described as extraordinary. The author criticises complex mathematical pursuits as unnecessary, emphasising the practical value of a good engineer over abstract calculations. The letter advocates for Morival, a noble and capable soldier, to be employed in the service of the sovereign, highlighting his skills, dedication, and loyalty. The author, nearing the end of his life, seeks comfort in the sovereign’s continued support for Morival, asserting that such support would be a just response to the injustices Morival has faced. Additionally, according to T. D. N. Besterman, the letter is certainly dated 2 January 1775.

The author presents a drawing of the Battle of Rosbac by d’Etalonde to the King, highlighting the profound admiration and dedication of an officer eager to serve in such battles. He expresses gratitude for the King’s support and the impact it has had on the officer’s loyalty, who is more focused on serving under the King than seeking any grace in France. The author commends the King’s ability to balance significant matters with personal attentiveness and reflects on the recent less impressive French coronation compared to the King’s impressive multifaceted leadership. He concludes with a declaration of lifelong loyalty and devotion to the King.

The writer expresses deep loyalty and admiration for the monarch and comments on the recent assassination attempt. He reflects on how the religious devotion of the conspirators did not prevent the natural sentiments of humanity from emerging, possibly due to the monarch’s virtuous influence. He believes that this atrocity will ultimately benefit the monarch by reinforcing their position and making rebellion appear shameful. The writer requests a brief response to his query and asks that it be sent to Geneva.