فَبِأَيِّ آلَاءِ رَبِّكُمَا تُكَذِّبَانِ
Which of your Lord’s favours will you both deny?
The refrain recurs across Sūrat al-Raḥmān, but the material before each occurrence changes. Thus identical wording is linked each time to its local subject matter, creating recurrence with discourse progression.
Avoid both extremes: calling it purposeless duplication and treating every occurrence as contextually identical. The text’s structure gives the refrain a cumulative, locally responsive function.