"The science that deals with things that transcend sensual perception (non-observable) and are generally little known. It deals especially with effects that cannot be explained by the universally known laws of Nature, but whose causes are still a mystery to those who have not penetrated deep enough into the secrets of Nature to understand them correctly. What may be occult to one person, may be fully comprehensible to another. The more the spirituality and intelligence of man grows and the more it becomes free of the attractions of sense, the more will his perceptive power grow and expand, and the less will the processes of Nature appear occult to him. What is occult is a mystery hence mysticism or the search to understand mystery or that which is occulted to view or understanding." [Hartmann, Franz; The Life of Philippus Theophrastus, Bombast of Hohenheim, Known by the name of Paracelsus and The Substance of His Teachings, George Redway, London, 1887]
Manly Palmer Hall
"Occultism is the ancient science which deals with the hidden forces of nature, the laws governing them, and the means by which such forces can be brought under the control of the enlightened human mind.
An occultist is one who believes in the reality of esoteric sciences, has studied them in a scholarly manner, has resolved to perfect his own consciousness according to their rules, and may, or may not, be able to practice the rituals and formulas of Transcendental Magic." [Manly Palmer Hall]
"The well informed student of occultism is one of the most universally learned of human beings. He must be acquainted with all of the important systems of world philosophy and religion, both eastern and western, and he must have a thorough understanding of ancient sciences and arts. There is no place for the superficial thinker in this field; and should he wander in by accident, it would be wise for him to depart in haste." [Manly Palmer Hall]
"Occultism is called in the mystic East the gupta vidya, the Secret Knowledge. It is not secret in the sense of being wilfully withheld, but by virtue of the same conditions in which differential calculus is occult or hidden to one who is just learning the multiplication table. It is not a body of knowledge that can ever be communicated by word of mouth or the written word. It is born in a man in proportion to his growth and power of fine response to all life. For it is the science of life, not only the science of life's material embodiments, and becomes the possession of the seer as his own being can grasp and respond to ever subtler and finer levels of being. H.P.B. has well defined it in an old issue of the magazine "Lucifer": "Occultism is not magic, though magic is one of its tools. Occultism is not the acquirement of powers, whether psychic or intellectual, though both are its servants. Neither is occultism the pursuit of happiness as man understands the word; for the first step is sacrifice, the second renunciation." Then she tells us what it really is: "Occultism is the science of life, the art of living."" [Clara Codd, The Way Of The Disciple]