In the book How is Knowledge of Higher Worlds Acquired?, the path to higher knowledge is presented, culminating in the encounter with the two guardians of the threshold.

This writing will additionally present the relationships the soul has with the various worlds as it progresses through the successive levels of knowledge.

As a result, we have what we can call Cognitive teaching of the hidden science, that is, the science that remains concealed in the usual way of knowing.

Instead of hidden science, we could say obscured science, because the results of this science do not remain hidden but are printed in books accessible to everyone.