In ancient tradition, humans are composed of body, soul and spirit. The body is our physical expression. The spirit animates the soul and the soul animates the body. In modern terms, the soul would be essentially our memory, since our memory contains snap shots and subroutines (habits) of our life, with this defining who we are. If you could swap your entire memory in a new body, the essence of you will appear in the new body.
The spirit animates the soul, implies that impulses; spirit, trigger the memory into action. If we are hungry, the feeling of hunger is not personal, but is part of the instinctive spirit of the human body. The need of the spirit; hunger, animates our memory, along the lines of the items, habits and routines we use for eating. These habits and choices are often specific to who we are; soul. We can also be animated by the spirit of the times, thereby using our meddle; memory, to extrapolate in real time.
The idea of the soul living forever, in modern terms, has a connection to the DNA. For example, if you were good at music; in your soul/memory, there is a good chance one or more of your children will have an innate propensity for music. Through the DNA, aspects of your soul are perpetuated.
Way back then, they did not have the science tools we have today to see the DNA and do brain scans. However, they were still able to observe and correlate human behavior, by looking inward and outward and correlate this in terms of three distinct layers, and how these connects to the DNA/eternity. Later science changes the nomenclature and essentially says the same things, but in a more modern and provable way. You need to learn how to interpret.
In Christian tradition, the souls of the departed, live forever, but are segregated to heaven or hell. If soul is our memory, habit and subroutine, this segregation is connected to the sum of good and evil habits and behavior. This are passed, forward, via the DNA. If this is true, one would expect to see both lambs; gentle, and wolves; aggressive people, in culture, due to long term conditioning of the human DNA. The idea was to get people to behave in a good way so the future will reflects a higher percent of good people in cultures, so it is easier to advance culture. In the USA and many first world countries, there are way more good people, allowing stability.