Reddit reviews Three Books of Occult Philosophy

I'd start with the book that played a large role in the revival of the modern occult: H.P. Blavatsky's The Hidden Doctrine, which is a synthesis of occult philosophies from all over the world.

Then, I'd go over the text on which all hermetic knowledge derives from; The Corpus Hermeticum by Hermes Trismegistus

I'd also reccomend looking into The Pistis Sophia, which explains the philosophies of early Gnosticism.

Another important text would be The Vision and the Voice by Aleister Crowley, which is an account of 30 visions that document how one may attain enlightenment, had by Crowley while he was performing a series of Enochian rituals out in the desert.

The Cosmic Doctrine by Dion Fortune is a book that was channeled by Dion Fortune, which she believes explains the hidden secrets and doctrine of the universe.

The Mystical Qabalah by Dion Fortune is a great book that explains the Qabalah, the system of philosophy which is the backbone of the occult.

This list would be incomplete without also including Agrippa's Three Books of Occult Philosophy, which was written by a Renaissance occultist named Henry Agrippa and is a foundational text to all branches of occult philosophy and knowledge.

The Dhammapada, The Questions of King Milinda, THE TÂO TEH KING, The Bhagavad Gita, The Upanishads, and The I-Ching are all also important philosophical texts to the occult. While they are not necessarily "occult" themselves, they all had a huge influence on the modern occult today, as well as many famous occultists such as Aleister Crowley, Dion Fortune, H.P. Blavatsky, etc.