The Mystical Qabalah is organised straightforwardly: introductory chapters on what the system is and how it should be approached, then a chapter on each of the ten sefirot in turn, working down the Tree from Kether to Malkuth, each treating the sphere's names, attributions, virtues, vices and correspondences and then discussing what working with it involves.
Its distinction is tone. Fortune writes clearly, in ordinary English, without the deliberate obscurity that characterises most of the material she is drawing on, and she says explicitly that she is publishing what previous writers concealed because concealment had begun to protect nothing but reputations. For a great many readers in the twentieth century this was the first Kabbalistic book that could simply be read.
Her framing is psychological as much as metaphysical. She presents the Tree as a map of the psyche and of the levels of consciousness, and treats the spheres as states to be entered rather than only as cosmic principles. That reading is a twentieth century one, formed in the same climate as depth psychology, and it is now so standard in English language occultism that its origin is easy to miss.
The Jewish Kabbalistic tradition it draws on is a separate and living one, described here rather than represented.