"The Mediums' Book sees Allan Kardec introduce and explain how human beings can communicate with the vast spiritual realm. Through this book, we learn how to contact spirits of human ancestors, and identify both the good and evil among them.
An excellent book of spiritual guidance, Kardec explains the methods of mediumship. How a seeker of the spirits can build an understanding of the practices needed to summon, and how the rituals must be carried out, is covered in many detailed chapters. Kardec is honest about the pitfalls; upsetting the spirits, or incurring the wrath and misfortune unleashed by malevolent spirits, is something a medium must always be cautious of.
In studying the behavior of the spirits, Kardec answers questions about whether they attach themselves to people or objects. We discover why spirits can manifest even without the presence of a learned medium; such as in haunted houses or other sites. Such appearances are shown to be important: sightings indicate man's willingness to gain affinity with spirits, and the need of spirits to communicate with the physical world.
We hear about the different types of medium, each of which are ideal for certain events. Some sorts of medianimity are used to form a bond with ancestor spirits, such as in meetings between families. Others are used to pacify bad spirits, or cleanse a haunted place of malevolent influences. Learning to write clearly is a needed skill – many mediums, in the midst of communing with the spirits beyond, receive messages that must be written down quickly.
Kardec reveals that there is a hierarchy of spirits, and that some spirits can be good or benevolent. Others, such as those who have suffered wrongs in life, can be evil or vengeful. The medium must not only distinguish the spirits' moral leanings, but also determine who they were by observing their language, the words they prefer, and how they view contact with living humans. Often, creating an affinity with a spirit takes time and care.
Allan Kardec spent years in groups conducting seances and rituals. With a background in the sciences, he knew the importance of recording what he saw, so that practitioners of mediumship could put this knowledge to use. In these meetings, he witnessed the practitioner make contact with spirits both good and bad; how they asked the spirit a question, or simply hear what it had to say."