The people of ancient Egypt believed that upon death, a person’s soul split into several parts, and continued to live on in an afterlife. Three of the more well-known forms of the spirit were the ba, the akh, and the ka.
The ba was the personality. It was shown as a bird with a human head— in particular, the head of the person to which it belonged.
The akh was represented by a type of bird called a crested ibis. At the moment of death, the akh left the body and flew to the stars to spend eternity in the heavens.
The ka was the life force, like our modern definition of a soul, and it looked exactly like its person.
The ka lived in the tomb for the rest of eternity. Personal possessions, such as furniture, weapons, and clothing, would be used by the ka in the afterlife, so these items were placed in the tomb with the mummy. Food and drink were also provided for the ka.
But the most important thing the ka needed was a body to inhabit. If the body rotted away, there would be no chance of an afterlife. It was therefore absolutely necessary to preserve the body as a mummy, since the ka still needed it. This is why the Egyptians made mummies for thousands of years. A mummy was the guarantee of eternal life.