An overt expression can be repeated after its referent is known to produce firmer establishment in the listener's mind. The name or descriptive title renews the subject's significance instead of allowing the referent to remain implicit.
In Qur'anic examples the question is why an explicit expression occurs where a pronoun would have been economical. One explanation is that the noun's independent meaning carries more force than the pronoun.
The effect does not emerge mechanically from repetition. It depends on the overt word's lexical content, the surrounding attribution and the aim of the discourse.