The highest eloquence does not arise merely from long sentences, rare vocabulary, or a large number of ornaments. Suitable diction, apt construction, force of meaning, and attention to the audience together produce rhetorical excellence.
Qur’anic expression is described as exhibiting a comprehensive excellence that even accomplished human speakers cannot reproduce in equivalent form. This is the claim of rhetorical inimitability. Literary expertise matters to evaluating its subtleties, as not every listener perceives technical nuances to the same degree.
The standard: unusually precise fitness between language and meaning, not obscurity or ornament as an end in itself.