 Despite burning his uncle's theological writings, Du Chastelet became a fervent Catholic; he believed that the Huguenots needed to be expelled from France, and his work frequently invoked God, and implored rulers to fight for a good cause and spare non-combatants; in his most famous work, he claimed to have learnt from battles he was involved in, which has been speculated to refer to the Fronde.His date of death is unknown, with some claiming that he died as early as 1670, only a short while after the 1668 publication of his "Traite de guerre, ou Politique militaire", but a more plausible estimate of his death is 1682.The "Traite de guerre" is notable for distinguishing between offensive and defensive warfare and for being compiled for Louis XIV of France.