Book excerpt: Master Cherng's translation of Discourse on Sitting and Forgetting, an 8th century classic text on meditation by Si Ma Cheng Zhen, is accompanied by his extensive explanatory commentary, unique in its ability to make this complex text accessible to the Western reader. In the introduction to the text, Master Cherng explains how to practice the Purification of the Heart method of meditation and photographs clearly illustrate the correct postures. He deciphers the Chinese metaphors and abstract language of Si Ma Cheng Zhen to give a clear explanation of the processes involved and the resulting changes to mind, spirit and body. His translation and explanatory commentary present the classic text in a way that can be easily understood and applied, allowing Western students of Daoism, and anyone with an interest in meditation, direct access to the meaning of this text in practice.