This book presented in English gard, is Book III of the first quarter, namely, the Kitab Asrsr al-Taharah (On the Mysteries of Purity). Though not one of the more profound contributions of al-Ghazali, it still remains an integral part of the Ihya and should not, therefore, be neglected.
Purity has four stages: The first stage is the purification of the body from excrements, impurities, and bodily growths, and discharges. The second stages is the purification of the bodily senses from crimes and sins. The third stage is the purification of the heart from blameworthy traits and reprehensible vices. The fourth stages is the purification of the inmost self (sirr) from everything except Allah. This last stages is that of the Prophets and saints. This book address the first stages of purity.