The book begins with the author's allegation that there is a school of thought which modern culture has forgotten, and that the metaphysics, and to a large degree the present physical science, "have been groping for centuries blindly after knowledge which occult philosophy has enjoyed in full measure all the while". Sinnett takes the liberty to express his belief that his knowledge is certainly true.

He argues:

"I have come into some contact with persons who are heirs of a greater knowledge concerning the mysteries of Nature and humanity than modern culture has yet evolved... Modern science has accomplished grand results by the open method of investigation, and is very impatient of the theory that persons who ever attained to real knowledge, either in sciences or metaphysics, could have been content to hide their light under a bushel.... But there is no need to construct hypotheses in the matter. The facts are accessible if they are sought for in the right way."

Sinnett explains that "the ultimate development" of an occultist requires him to comply with "absolute physical purity". The candidate is obliged from the beginning to provide evidence that he is willing to comply with this requirement. Throughout the trial period, he should observe complete celibacy and refrain from all physical pleasures. However, this way of life does not presuppose any particular rigid discipline or hard asceticism, or "withdrawal from the world". The author says:

"There would be nothing to prevent a gentleman in ordinary society from being in some of the preliminary stages of training for occult candidature without anybody about him being the wiser. For true occultism, the sublime achievement of the real adept, is not attained through the loathsome asceticism of the ordinary Indian fakir, the yogi of the woods and wilds, whose dirt accumulates with his sanctity - of the fanatic who fastens iron hooks into his flesh, or holds up an arm until it is withered."