Ancient Egyptian religion is often called a “death cult”, and there is much truth in this. So much of the activities and wealth of both rich and poor was connected to death. Tombs were built as large and adorned as the owner could afford, and anyone with the funds prepaid for mummification.
The reason for this heavy focus on death relates to the image of the world divided into two halves, which together formed the eternal continuity of cosmos.

Yes, this sounds confusing to most modern people, but it was the unquestionable truth to the ancient Egyptians.

The sun was the guide for this cycle. During day, the sun passed over the world of the living. During night the sun entered the other world, the other part of cosmos, the world located beneath the ground of man.
And this is a central fact to understanding the shape of tombs, especially the finest ones, the royal tombs on the west bank of the Nile at Luxor. Here the pharaohs and queens built their staging posts for joining the eternal cycle of the sun. Hence it was important to drill into the ground, getting as good a position as possible to join nothing less than the Sun.