Acharya Prashant explains that spirituality means 'knowing completely,' which involves understanding the mind and its relationship with the external world. He describes that while an ordinary person sees only the world, a wise person perceives three elements: the world, the observer, and the witness. The witness is the one who remains unaffected and detached, observing both the external event and the internal reaction. This state of witnessing is our true identity because, unlike the mind and the world which are constantly changing, the witness remains constant and unchanging. He emphasizes that being a witness does not mean leaving the world, but rather living in it without being gripped or affected by its turmoil, much like a person navigating through traffic without getting hit.