From the most remote period theology alone regulated the march of philosophy. What aid has it lent it?

It changed it into an unintelligible jargon, which only had a tendency to render the clearest truth uncertain; it converted the art of reasoning into a science of words; it threw the human mind into the aerial regions of metaphysics, where it unsuccessfully occupied itself in sounding useless and dangerous abysses. For physical and simple causes, this philosophy substituted supernatural causes, or, rather, causes truly occult; it explained difficult phenomena by agents more inconceivable than these phenomena; it filled discourse with words void of sense, incapable of giving the reason of things, better suited to obscure than to enlighten, and which seem invented but to discourage man, to guard him against the powers of his own mind, to make him distrust the principles of reason and evidence, and to surround the truth with an insurmountable barrier.

In Meslier’s time, philosophy had been weaponized into a tool for refuting the truth-claims of religion. The catholics and protestants had been fighting over a theological problem (can a mere human interpret god’s will accurately?)   As Popkin explains* it, philosophy became the tool for epistemological challenges against claims of knowledge of god. Corrosive skepticism destroyed epistemological claims, leaving philosophy in disrepute and religious faith smoking and leaking below the water-line.

Meslier is lamenting that the weapon that sectarians used to injure eachother, laid waste to religion in general. “A plague on both your houses!”

(* See Popkin “History of Skepticism from Savanarola to Bayle“, which is a recommended reading book)