Marvels of the Heart is thought to be the key volume of the 40-book Ihya' 'Ulum-Al Din—Revival of the Religious Sciences—, the most read work in the Muslim world after the Qur’an, and considered by many to be the Summa Theologica of Islam. These traditional teaching stories, which use the theme of the heart as a mirror, illustrate key tenets of Islam on the requirements of religion, living in society, and the inner life of the soul.