The people of Ancient Egypt believed that when a person died their soul split into two parts. The Ba would leave the body each morning to keep watch over the person's living family. The Ka would fly off to the Land of Two Fields which was their afterlife. Each night both the Ba and Ka returned to the body in the tomb to rest for the next day. A cartouche on the coffin helped the Ba and Ka find their way back. However if the preserved body was disturbed or damaged the Ba and Ka would be lost and a person would cease to exist in the afterlife. That is why grave robbery was considered such a vile crime and punishable by death.
Ancient Egypt page