A classic modern occult work, I would imagine composed in the early 20th Century; many have suspected the author is in fact William Atkinson and having read several of his books I would agree there is a similar style and approach. It begins:
The purpose of this work is not the enunciation of any special philosophy or doctrine, but rather is to give to the students a statement of the Truth that will serve to reconcile the many bits of occult knowledge that they may have acquired, but which are apparently opposed to each other and which often serve to discourage and disgust the beginner in the study. Our intent is not to erect a new Temple of Knowledge, but rather to place in the hands of the student a Master-Key with which he may open the many inner doors in the Temple of Mystery through the main portals he has already entered.
The entire book is written in a stuffy but readable Edwardian mode. It is mostly commentary on seven principles:
1. The principle of mentalism
“The All is Mind; the Universe is Mental.”
2. The principle of correspondence
“As above, so below; as below, so above.” […] This principle embodies the truth that there is always a correspondence between the laws and phenomena of the various planes of being and life.”
3. The principle of vibration
“Nothing rests; everything moves; everything vibrates.”
4. The principle of polarity
“Everything is dual; everything has poles; everything has its pair of opposites; like and unlike are the same; opposites are identical in nature, but different in degree; extremes meet; all truths are but half-truths; all paradoxes may be reconciled.”
5. The principle of rhythm
“Everything flows, out and in; everything has its tides; all things rise and fall; the pendulum-swing manifests in everything; the measure of the swing to the right is the measure of the swing to the left; rhythm compensates.”
6. The principle of cause and effect
“Every cause has its effect; every effect has its cause; everything happens according to law; chance is but a name for law not recognized; there are many planes of causation, but nothing escapes the law.”
7. The principle of gender
“Gender is in everything; everything has its masculine and feminine principles; gender manifests on all planes.”
I would describe it as a work of philosophical occultism; there are no practical techniques here. In essence, it treats of cosmic laws, and their manipulation. Hermetic occultism is about transcending our mundane reality, in order to see and be more, and to thus control the lower:
We overcome the lower laws, by applying still higher ones – and in this way only, But we cannot escape Law or rise above it entirely.
Having studied the occult for a decade and more, I found much of it obvious; though I can’t say if that is because the Kybalion’s themes have been so echoed in subsequent works, or because it borrows from earlier works, or both. However, it would be an interesting read for anyone beginning to study the philosophical occult; and even I found much of interest, e.g.
The word Positive means something real and strong, as compared with a Negative unreality or weakness. Nothing is further from the real facts of electrical phenomenon. The so-called Negative pole of the battery is really the pole in and by which the generation or production of new forms and energies is manifested. There is nothing “negative” about it. The best scientific authorities now use the word “Cathode” in place of “Negative,” the word Cathode coming from the Greek root meaning “descent; the path of generation, etc.” From the Cathode pole emerge the swarm of electrons or corpuscles; from the same pole emerge those wonderful “rays” which have revolutionized scientific conceptions during the past decade. The Cathode pole is the Mother of all of the strange phenomena which have rendered useless the old textbooks, and which have caused many long accepted theories to be relegated to the scrap-pile of scientific speculation. The Cathode, or Negative Pole, is the Mother Principle of Electrical Phenomena, and of the finest forms of matter as yet known to science.
For the time, pre-WW1, this is an interestingly Taoist insight.

That is, that lack itself generates, by its very lack & vacuum, an enabling suction. Imbalance is the driving force for balance. As in The Four Quartets, the perfect figure is found not in static being but rather in becoming; in the ceaseless motion of death and rebirth, striving and becoming, failure and regeneration.
https://www.youtube.com/watch?v=Ugc5FZsycAw