The forty-four Letters to Friends of the Spirit were sent in five languages in the form of "Briefs," on a weekly basis, during the periods of restricted freedoms in 2021, to members of initiatory, Masonic, Martinist, Gnostic, Pythagorean, Rose-Croix, Swedenborgian, and other organizations in order to support practice. It is a meandering through the traditional world, the unique golden thread of which is nonduality. A stroll through a labyrinth of doors. Rather than a teaching, which it is not, this book can be seen as a set of footnotes referring to the knowledge that each of us carries within. Everyone is the best expert of their own realization. It's just a matter of attention. As for the rest, it's not nothing: it is companionship, spiritual friendship and shared regard. Among the topics covered are: prayer and meditation, the meaning of prophecies, the use of Hebrew, the myths of chivalric traditions, the temple and the crypt, the theurgy of the Élus Coëns, the secret grammar, geometry, alchemy, the Arcana Arcanorum, the work of Swedenborg, and the contribution of literature to initiation. Hidden in the heart of these letters, you will find a Little Treatise on the Christification of Beings. This treatise on a direct way within the Christian tradition escapes the tension inscribed in the Gospels between the Judeo-Christian and the Pagan-Christian poles to approach the essential, in which cultural and historical forms are traversed, leaving room for the Spirit.