Final answer:
Cleante's concern in the passage references the theme of religious hypocrisy in Molière's play "Tartuffe," which also casts light on related themes such as blind faith, deception, and misplaced trust.
Step-by-step explanation:
Cleante in the passage is expressing a concern that aligns with the theme of religious hypocrisy. This theme is prominent in the play "Tartuffe" by Molière, where the eponymous character Tartuffe presents himself as a pious and devout individual, while in reality, he is a con man exploiting the gullibility and blind faith of his benefactor Orgon. The concern about the evil leading people astray with its 'flattering and often brilliant exterior' directly speaks to the idea of characters being duped by appearances, thus also touching on themes of deception and misplaced trust.