Although not immediately apparent, the following books form part of the teachings of ancient systems of knowledge known as the Mysteries, the pursuit of which has been sought by the curious for millenia, often via gnostic societies  — Neoplatonists, Rosicrucians, Scottish Rite Freemasonry, to name a few.

The understanding and application of the Mysteries teachings has been regarded by philosophers and seekers as the highest level of spiritual achievement, for one very good reason: they lead to the discovery of the true nature of reality and the soul.

As true then as it is today.