The source examines a subtle issue: when the subject is emphasized, what precisely is fixed more firmly in the hearer's mind? One analysis stresses the referent or meaning of the subject; in some formulations the predication itself is strengthened as well.
«جاءني زيد زيد» — repeats the subject name to secure identification.
«إن زيدًا جاء» — «إنّ» reinforces the proposition as a whole.
«أنا نفسي سمعت» — explicitly singles out the speaker as agent.
These constructions should not be collapsed into one type. Emphasis on the subject and emphasis on the reported judgment have different immediate targets, even if their effects overlap in a context.