Can you describe how Chapter 19 defines the Supreme Being, Brahman, and the subtle layers of existence?

Chapter 19 presents a profound description of the Supreme Being, identifying Shri Sai with Brahman, the reality that resides in everything from the smallest atom to the vast universe. It establishes a hierarchy of subtlety in existence. The text explains that the Soul (Atma) is a Great Power. Subtler than the Soul is the Unmanifest (Avyakta), also called Maya or Unmanifest Nature. Even subtler than all these is the Purusha, the Supreme Being. This Purusha is described as the ultimate goal where the senses and mind finally find rest. Chapter 19 explicitly states that this ultimate state, the Purusha, is indeed the Pure Brahman, the formless, changeless, and self-luminous pure consciousness.