It differentiates him from his fellow creatures in the animal kingdom. Without the ego, man would possess no permanency. Therefore, he would act upon a thing only once, and there would be no repetition of the action. Each time he met the same situation he would need to learn how to react to it again. Without the ego there would be no memory of hunger, thirst, or other things.
Memory develops at various stages and is identified by other terms.
Memory is first called an astral body when the mental image is just visualized. For example, when a person sees a pencil, then quickly turns away and retains the pencil's image. The mental image becomes knowledge when it is retained. An example of this is when the image can be brought back into memory without the pencil actually being perceived. What gives this knowledge or memory permanency can be designated as soul .