Can you explain the concept of Brahman and the Soul as detailed in Chapter 19, including the hierarchy of subtlety?

Chapter 19 presents a deep philosophical view of Brahman and the Soul. It identifies Sai as the Brahman that resides in everything, being 'subtler than the subtlest and greater than the greatest.' The chapter then describes a hierarchy of existence based on subtlety. The Soul (Atma) is a Great Power. Subtler than the Soul is the Unmanifest (Avyakta), also called Maya. Finally, subtler than all of these is the Purusha, or the Supreme Being. This Purusha is identified in Chapter 19 as the ultimate goal and the Pure Brahman, where the senses and mind finally find rest.