«نِعْمَ رَجُلًا»
What an excellent man! (part of a conventional formula of praise).
Grammatical accounts of this construction can posit a covert or unspecified pronoun, which is clarified by the following accusative tamyīz (تمييز). The relation between an initially implicit reference and its later explanation contributes to the formula's expression.
For the rhetorical lesson, the key insight is that an agent need not always appear as a straightforward overt noun at the earliest position. Some forms proceed from an initially general reference to explicit clarification.
Detailed syntactic disagreements should not be collapsed into one universal analysis; they are beyond the immediate passage's rhetorical objective.