Inquiry into the world: the wise man sees the entire universe as no more substantial than a dream remembered upon waking
This opens a shift in the text's approach — instead of describing the liberated mind's qualities, chapter nineteen turns to examining the status of the world itself.
After the long eighteenth chapter's portrait of how a self-realized person lives, the brief nineteenth chapter changes the angle of inquiry to ask what the world actually is, once examined honestly. Its answer draws on a comparison Indian philosophy returns to often: the entire universe of sensory experience, however solid it feels while you're in it, has no more independent substance than a dream does while you're dreaming it. The comparison isn't meant to prove the world is unreal in some nihilistic sense, but to relocate its reality — vivid within experience, yet without existence apart from the awareness in which it appears. This inquiry sets up the chapter's central move toward seeing the world as appearance rather than as separately existing substance.
The dream analogy for everyday experience is also central to Gaudapada's Mandukya Karika, an earlier Advaita text arguing that waking and dream experience are equally unreal from the standpoint of ultimate truth.
Ashtavakra Gita