Hey, I'm not sure what the best book to read would be... but I'll chip in my :twocents: in case they help!
Originally the word soul just means principle of life. Because of this both plants and animals are said to have souls as well as humans. Often when people talk about the soul today they are referring to the eternal soul of humans.
The connection between the soul and the individual is very close, because of this, many people have been led to say that people are souls, thinking of the human body as merely extrinsic to the person. However, if that were the case, death would not be a punishment in any respect, as it would simply be the removal of something extrinsic to the person which prevents it from existing as it ought to by its nature. Which means that both the body and the soul are important parts of each individual. The soul is more important as it is the principle of our life as humans, but it is a part of the nature of the soul that it is meant to exist with a body so as to complete each person as an individual human. So the soul of each human is the immortal and immaterial part of them.
This is only a beginning... there is so much more to the understanding of the soul than this, its dignity, etc. I think I might keep an eye on this thread so I can use some of the recommendations myself!;)