One must know that the body and the world are part of the mirage. The mirage appears and disappears to the formless witness. The witness of the mirage is formless and eternal.
When there is mirage then there is duality. When there is no mirage then there is only non-duality. The non-duality is independent and duality is dependent on non-duality. The duality is impermanent and non-duality is permanent and eternal. The individual experiences of birth, life and death is part of the mirage. Thus believing in birth, life and death and judging on the physical base keeps one in the grip of illusory pleasure and sorrow.
All the experiences such as astral travel, visions are mere mirage, because they exit only in the realm of duality. The waking/dream/visions/astral are created out of formless clay.
The formless clay is real and eternal not the forms and shapes created out of it.
