On every occasion it indicate towards a special part of...
On every occasion it indicate towards a special part of loftiness of this incident and desires that every time it should invite the attention of the people to an special aspect which has not been indicated other times. It is a reality that can be realized only if you ponder upon the stories of the Holy Quran.
The verses that are repeated on other occasion (for example Surah Rahman the verse of: which then of the bounties of your Lord will you deny?) is for the purpose to create a psychological effect on the hearers. When the Almighty desires to exhort people He repeats to them again and again those points which have special psychological and emotional aspect.
For example in the same Surah Rahman the Almighty Allah enumerates some important bounties that have fundamental effect on the formation and continuation of human society. And in the same the major bounties are mentioned; that are arranged for man in the hereafter. The aim of enumerating those bounties is to awaken the emotions of man.
Allah repeats the sentence: Which then of the bounties of your Lord will you deny, so that people develop the ability to recognize truth and it prepares him to submit to the truth and develops his humanity and feelings. Therefore the repetition of this type is itself necessary from the point of view of guidance and it does not in any way mar the eloquence of Quran, rather it is counted as the beautiful discourse because it first of all becomes the cause of emphasis and effect.
This type of repetition is widely seen in the Urdu, Arabic and Persian literature. And there are numerous examples of Arabic Panegyric (Qasida) which are designed on the repetition of one sentence or stanza. One such example is the Qasida of Adi bin Rabiah the uncle of Imrul Qays, which he composed in the memory of his brother, Kaleeb. The sentence Alaa Laisa Adlam min Qaleeb is repeated twenty times. And of the Urdu poets, especially in Dr Iqbals poetry we find such examples of repetition.