Although I don't remember much repetition except at few places like sura Rahman for instance, but repetition in general implies significance or importance, just like we say it again and again to our kids, the things that w want them to remember.
Philosophy is your question relate to repetition of a particular Ayat in a particular Surah (like in Surah e Rehman) or repition of a topic (like Hazrat Moosa's topic) on different places of the Quran?
Islam and Quran/Arabic aren't spread independently of each other.
It is the shortcoming of the ummah that we put little to no importance on the learning of Arabic or Islamic traditions in the childhood syllabus. We are capable of learning so much and so many languages but somehow just learning to read the Quran in Arabic without understanding is all we can manage? We get so excited about learning other languages so why the reticence to Arabic?
Although I don't remember much repetition except at few places like sura Rahman for instance, but repetition in general implies significance or importance, just like we say it again and again to our kids, the things that w want them to remember.
And the kids who are spoiled or are rebelious, hate that reptetion. So, rebelious souls among us also hate God's repetition :(
@Op: besides what TLK said, in answer to your second point, it's not God who forgets, it's us who have tendency to forget so God repeats certain important things over and over so we remember.
It is also important to keep in mind that Quran is not a Book that was written by someone in a leisure time. It is words of God and more accurately, these are orations/sermons of God. Nature of sermons is such that things are repeated so that listeneres keep the message in mind.
^ also keep in mind that God knows that none of us would complete the quran in one sitting. Its like city posting "smoking is dangerous for your health" signs all over the city. We can argue that hey, I saw that sign already on 5th street, why did they re-did that on 10th street. Well, the answer is
Because its good to remind again and again
also, what if someone only drives through 10th street only. If the sign was only on 8th street, he would never come to know.
One reason which I think, that is the most common words are used in Quran are 'Wa-Qaloo, (they said), 'Yasaloonaka (they asked)' and 'Qul (tell, inform them, say to them)' etc., It is like Question and Answer session between non-believers and Almighty God through his Prophet Muhammad PBUH. Because the terms 'the said, they asked, and to told them, inform them, say to them' will not be completed without a messenger in between both. Revelation of verses depends on time, place and its occurance.