The only people who got mummified was an Egyptian who could afford to play the expensive process of preserving their bodies for the after life
They mummified people because The ancient Egyptians believed that when someone died, their soul left their body. The soul would then return and be reunited with the body after it was buried. However, the soul needed to be able to find and recognise the body in order to live forever.
Boak, Arthur E. R. The History of Our World. Boston: Houghton Mifflin, 1959. Print.
Mummification. Brooklyn: Museum, 1994. Print.