Quran is a cure for the hearts

The Qur’aan is a cure for that which within the heart, and for the one who has the sickness of doubt and desire in his heart, for it contains clear proofs that distinguish the truth from falsehood, and remove the sickness of false doubts to leave certain knowledge, correct perception and understanding such that the heart sees things in accordance to their reality. It contains wisdom, goodly exhortations both encouraging good and deterring from evil, and stories which contain lessons that necessarily lead to the correction of the heart by making the heart desire what is good for it and detest what is harmful to it. Hence the heart is left desiring that which will guide it, hating that which will deviate it after it used to desire that which would deviate it and hate that which would guide it.