An utterance conveys a basic propositional content and may also provide an additional rhetorical implication through its choice of construction.
“Zayd came” states a coming; “It was Zayd who came” adds a specification or exclusiveness that is not automatically suitable in every situation. Whether that additional implication serves the intended occasion is a distinct question.
The example shows why an analysis of balagha must consider both what is said and how the wording's special features serve the context.