Option 1 -> Faithless means disloyal or untrustworthy, which relates to reliability and faith, not complexity or difficulty of understanding.
Option 2 -> Facile means easy or superficial, which is actually the opposite of recondite.
Option 3 -> Simple means uncomplicated or easy to understand, which directly contrasts with the meaning of recondite.
Option 4 -> Abstruse means difficult to understand or obscure, which perfectly matches the meaning of recondite.
Hence, Option 4: Abstruse -> Both "recondite" and "abstruse" describe something that is obscure, difficult to comprehend, or dealing with profound and specialized subject matter -> correct