The source discusses a familiar grammatical convention: the modifier of an indefinite serves takhṣīṣ (restriction), while the modifier of a definite serves tawḍīḥ (clarification). Rhetoric asks why the speaker requires that effect on this occasion.
Modified nounGrammatical descriptionResult for the hearer
IndefiniteRestrictionThe possible class is narrowed
DefiniteClarificationThe intended known referent is identified
Thus «رجلٌ عالمٌ» limits the class, while «زيدٌ التاجرُ» disambiguates a known name. The syntactic relation and its rhetorical purpose are connected but not identical.