«والبلاغة: في اللغة الوصول والانتهاء»
Lexically, balāghah denotes reaching and arriving at an endpoint.
The root b-l-gh expresses arrival or attainment. In ordinary usage, “balagha fulān murādahu” conveys that a person achieved an intended end. This provides the lexical background of the technical term.
The technical discipline does not merely ask whether sounds reached someone's ears. It requires an eloquent utterance expressed in a form appropriate to the circumstances. Arrival is the lexical core; contextually suitable expression is the rhetorical question.