Volume III — The Book of the Heart (Kitab Sharh Aja'ib al-Qalb)

The third volume of the Ihya — the 'Rub' al-Muhlikat' (the Quarter of Things That Lead to Ruin) — opens with the Book of the Wonders of the Heart (Sharh Aja'ib al-Qalb), which is arguably al-Ghazali's most original and psychologically sophisticated contribution to Islamic thought. In this book, he develops a comprehensive Islamic psychology of the heart (qalb) — understood not as the physical organ but as the spiritual center of human consciousness, will, and moral character.

Al-Ghazali draws on the Quranic declaration: 'Truly it is not the eyes that are blind, but the hearts within the chests' (Quran 22:46) and the famous hadith: 'Truly in the body there is a morsel of flesh. If it is sound, the whole body is sound; if it is corrupt, the whole body is corrupt. Truly it is the heart.' (Al-Bukhari and Muslim.) These two texts establish the heart as the decisive reality in a human being — the faculty that determines whether a person is, in the deepest sense, alive or dead.

Al-Ghazali describes the heart as simultaneously the site of human nobility and the site of human vulnerability. It is the place where faith resides, where divine knowledge settles, where love of Allah is kindled, and where the relationship with the divine is ultimately mediated. But it is also the seat of all the spiritual diseases — arrogance, envy, hypocrisy, love of the world, forgetfulness of Allah — that constitute, in the Quranic view, the real human illness. Physical illness is a minor matter compared with the illness of the heart: 'In their hearts is a disease, and Allah has increased their disease' (Quran 2:10).

The metaphysics of the heart in al-Ghazali's account is subtle. He argues that the heart has two orientations: toward the divine world (al-'alam al-malakut), from which it receives light, guidance, and inspiration; and toward the world of physical nature (al-'alam al-mulk), from which it receives the impressions of sense experience and desire. The battle between these two orientations is the battle of the spiritual life — and the victor is determined by which faculty the person habitually feeds. A person who spends their time in heedlessness, entertainment, and unrestricted desire gradually darkens the heart's receptivity to the divine world; a person who habituates themselves to remembrance of Allah, reflection on the Quran, and struggle against their lower desires gradually polishes the heart until it can receive the light of divine proximity.

This chapter also introduces al-Ghazali's account of the 'armies of the heart' — the various faculties (anger, desire, rational thought, imagination) that can either serve the heart in its journey toward Allah or pull it in the direction of ruin. Each faculty has its proper function within a well-ordered soul; spiritual ruin comes not from having anger or desire but from allowing them to dominate reason and religious commitment. The soul (nafs) is the commanding self that must be disciplined — the Quran describes the great struggle (jihad al-nafs) against the soul's lower inclinations as the supreme jihad.