A predicate may be a single constituent or a whole clause. When a subject is mentioned first and followed by a clause containing a pronoun linked to it, the arrangement may reinforce the assertion.
«زيد أبوه منطلق»
Zayd—his father is setting off.
«أبوه منطلق» functions as the clause predicated of «زيد». The pronoun in «أبوه» links the inner clause back to the fronted subject. That makes this structure different from a direct simple predicate.
The source distinguishes what the inner predication directly concerns from the outer theme being introduced. Both levels must be identified before assigning a rhetorical function.