"Allah has sent down the best statement, a Book (this Qur'an), its parts resembling each other in goodness and truth, oft-repeated. The skins of those who fear their Lord shiver from it (when they recite it or hear it). Then their skin and their heart soften to the remembrance of Allah. That is the guidance of Allah. He Guides therewith whom He pleases and whomever Allah sends astray, for him there is no guide."
(Surah 39: Az-Zumar (The Groups); verse 23)