Quran is so concise but in Surah Rahman a single ayah repeated 31 times

We know Quran is a concise book, not a single word there is without reason. Every single word is decorated and managed like a pearl in necklace, and not a single word wasted but when you see the **Surah Rahman** a single ayah "Fabe-aiye alae ..." repeated 31 times. What could be the reason of using it again and again?