Why did the Egyptians believe that the country would exist while the pharaohs ruled them?

Because the pharaohs were considered substitutes for the gods. People believed that if Pharaoh was happy and healthy, then everything on Earth would be fine. If, on the contrary, you need to wait for trouble. The death of the pharaoh was considered the greatest grief. People mourned the deceased for about a month. If people wanted to appease the gods, they asked the pharaoh to convey their requests to the inhabitants of heaven. Also, people brought gifts to the gods so that they were always supportive and fulfilled their prayers. People believed that the pharaoh could control the Nile and the harvest. Therefore, they in every possible way took care of good relations with their ruler.