Affirming the true Teacher
The phrase is understood as the predicate informing about الرَّحْمَٰنُ. With the subject placed first, Arabic rhetoric calls this al‑ithbāt ʿalā ghayr al‑fāʿil—a form that emphatically affirms: It is truly Ar‑Rahman who taught the Qur’an, refuting claims that a human taught the Prophet.