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Ancient Egyptians believed that death occurs when a person's ka leaves the body. Ceremonies conducted by priests after death, including the "opening of the mouth (wp r)", aimed not only to restore a person's physical abilities in death, but also to release a Ba's attachment to the body. This allowed the Ba to be united with the Ka in the afterlife, creating an entity known as an "Akh" (3ḫ, meaning "effective one").
Egyptians conceived of an afterlife as quite similar to normal physical existence — but with a difference. The model for this new existence was the journey of the Sun. At night the Sun descended into the Duat (the underworld). Eventually the Sun meets the body of the mummified Osiris. Osiris and the Sun, re-energized by each other, rise to new life for another day. For the deceased, their body and their tomb were their personal Osiris and a personal Duat. For this reason they are often addressed as "Osiris". For this process to work, some sort of bodily preservation was required, to allow the Ba to return during the night, and to rise to new life in the morning. However, the complete Akhu were also thought to appear as stars. Until the Late Period, non-royal Egyptians did not expect to unite with the Sun deity, it being reserved for the royals.
The Book of the Dead, the collection of spells which aided a person in the afterlife, had the Egyptian name of the Book of going forth by day. They helped people avoid the perils of the afterlife and also aided their existence, containing spells to assure "not dying a second time in the underworld", and to "grant memory always" to a person. In the Egyptian religion it was possible to die in the afterlife and this death was permanent.
The tomb of Paheri, an Eighteenth dynasty nomarch of Nekhen, has an eloquent description of this existence, and is translated by James P. Allen as:
Your life happening again, without your ba being kept away from your divine corpse, with your ba being together with the akh ... You shall emerge each day and return each evening. A lamp will be lit for you in the night until the sunlight shines forth on your breast. You shall be told: "Welcome, welcome, into this your house of the living!"
Read more about this topic: Ancient Egyptian Concept Of The Soul