Throughout the play, Cleante is presented as the voice of reason. He sees through Tartuffe straight away; he knows that beneath his pious, earnest exterior, there beats the heart of a cunning charlatan. Realizing that Orgon is being used and exploited by Tartuffe for personal gain, Cleante confronts his brother-in-law and, in one telling passage of his brief monologue, asks him a particularly probing question:

Is it possible that a man can be so bewitching at this time of day as to make you forget everything for him?

Thus speaks a man of the Enlightenment, an intellectual movement of the seventeenth and eighteenth centuries which laid the foundations of modernity. The Enlightenment privileged reason as the sole means of acquiring knowledge. Among other things, this made it a threat to established religion, which sought to base knowledge primarily on divine revelation.

We can see this valorization of reason in the above quotation. Cleante is implying that Orgon, in allowing himself to be bewitched by Tartuffe, hasn't been been using his innate capacity for reasoning. Instead, he's simply deferred to what he believes is Tartuffe's superior spiritual authority.

Cleante's admonition reflects Enlightenment thinkers' attacks on the unthinking acceptance of religious authority, which they believed was based on fear and ignorance rather than truth as they understood it.