The heretic Pharaoh Akhanaten and his wife Nefertiti have foolishly turned their backs on the Egyptian gods to embrace the monotheistic faith of Atenism. He has declared himself the son of Aten and has outlawed the worship of all other deities, bringing his population into heresy. Outraged at this betrayal, the gods have cursed all of humanity with what has come to be known as the undying plague, and closed off the afterlife to humans. From then on, all people who die will arise a few days later as a mindless zombie. Prevented from passing on to the next life, they suffer the eternal anguish of undeath and an intense craving for flesh.
However, the heretic pharaoh has discovered a forgotten ritual that leads to true immortality. After a person dies, their body is embalmed and then mummified during this ritual, conducted by the priests of Aten. When the person inevitably rises, they retain their original faculties as when they were alive. The magic of the ritual sustains their bodies and prevents them from breaking down. The heretic pharaoh and Nefertiti themselves become liches through this ritual due to them having divine status. They commission for a magical wall to be built around Egypt, protecting it from the outside world.
Current Egyptian society is as follows:
Liches- this encompasses the king and queen, their relatives, priests, and anyone they consider necessary to preserve the new faith and prove themselves useful. Their bodies represent perfect undeath and are eternal and never break down, requiring no form of mummification.
Mummies- these are the common citizens who are the followers of Atenism. They have proven themselves worthy in life and have been rewarded with a lower form of undeath. Although mummification sustains their bodies through magic, they suffer wear and tear and must be periodically repaired.
Living humans- these flesh and blood individuals go through life proving their worthiness to society. Now that the afterlife is barred to them, they must show their faithfulness and loyalty to be granted eternal life, or risk suffering the curse in death.
Zombies- these pitiless souls are made up of individuals who were not mummified and are forever cursed to walk the earth in agony. They suffer eternal hunger and waste away in a state between life and death, never to know peace for the rest of time.
Mummification is expensive, the ancient ritual more so. This means that it would be primarily done to the most valuable people, with most others becoming zombies. For society to function, I need everyone to believe that everyone has an equal shot at an immortal afterlife, else they will rebel against the social hierarchy. How can I make this possible?