All perfect praise be to Allaah, The Lord of the Worlds. I testify that there in none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Is it wrong to ask this question and it is not suitable for any Muslim who read the Quran only once to ask this question. We say this because most of the verses of the Quran are only mentioned once, and only very few verses were repeated, like for example, the Saying of Allaah (which means): {Woe that Day, to the deniers (of the Day of Resurrection)}. Which is repeated 10 times in chapter 77, and mentioned in few other chapters, and His Saying (which means): {So which of the favours of your Lord would you deny?} which is repeated 31 times in chapter 55. Allaah, Exalted is He Says (what means): {He is not questioned about what He does, but they will be questioned.}[Quran 21:23]. So, a Muslim should not ask why a given verse is mentioned only once or why another verse is repeated many times
Allaah Knows best.