Spirit world is the fourth dimensional world. Where people live on the astral planes or heavenly fields of existence. Therefore this is where we all go; after passing from earthly existence with death. Similarly the Tibetan book of the dead is a very old esoteric book which describes the process of dying.
The Tibetan book of the dead describes the process of dying; with guidance to afterlife. It is stated in the Lord’s prayer. That as it is on earth, so it is in heaven. We all remain the same person in the fourth dimension. With the only difference being in heaven; we do not have a physical body.