This book arose from the need to understand, with historical and doctrinal rigor, who this central figure, so little studied in a comprehensive way, really is. Although his name is scattered throughout Kardec's works, especially those of a moral and instructive nature, never before, to our knowledge, has the systematic work of gathering all the direct quotations, contextual references, and messages signed by this Spirit in the 22 fundamental works of Allan Kardec been carried out. This study, therefore, offers the reader a panoramic and at the same time meticulous view of the role that the Spirit of Truth plays in the Third Revelation.

This analysis does not intend to speculate beyond what the doctrine allows. Its purpose is to respect the Kardecian method: observe the facts, gather the evidence, compare, and then conclude. The result is a logical and profoundly coherent picture: the Spirit of Truth is more than a collaborator; it is the direct link between Christ and Spiritism, the source that illuminates, coordinates, and authenticates the teachings revealed to humanity in the current phase of its progress.

As the reader peruses the book, they will realize that the Spirit of Truth is not limited to an inspirational function; that he acts as the spiritual director of the Spiritist doctrine, guaranteeing its unity and fidelity to the morality of the Gospel; that his message is essentially moral, but sustained by natural law, destined for the renewal of humanity; that his discourse bears an unequivocal identity with the thought of Christ; and, finally, that, as protector of Allan Kardec, his direct assistance was constant.