The great 11th-century Islamic scholar Imam al-Ghazali (may Allah have mercy on him) is a jurist and Sufi scholar who left profound marks not only in his own time but in almost every century through the works he authored. Among these valuable works is Ihya' Ulum al-Din, which has been deeply respected and accepted throughout the Islamic world in the fields of jurisprudence, ethics, and Sufism since the day it was written. This timeless work, translated section by section into independent books by Prof. Dr. Dilaver Selvi and published by Semerkand Publishing, draws attention with both its translation language and its design. The 21st book of the series, "States of the Heart," explains with sources and evidence many topics such as the meanings of the words self (nafs), spirit (ruh), heart (qalb), and intellect (aql) and what is intended by these terms, the special nature of the human heart, the explanation of the qualities gathered in the heart, Satan’s assault on the heart through whispers (waswasa), the meaning of whispers and the reason for them overcoming the heart, and the ways Satan enters the heart.