[1] It was the first theosophical work by the author; according to Goodrick-Clarke, this book "gave sensational publicity to Blavatsky's phenomena" and the letters from the mahatmas, and drew the attention of the London Society for Psychical Research.

In February 1881 Kuthumi, writing that he is interested in Sinnett's book and its success, gave permission to use his letters: "I lay no restrictions upon your making use of anything I may have written to you..., having full confidence in your tact and judgment as to what should be printed and how it should be presented.

[13] Kuthumi wrote: "When the first hum and ding-dong of adverse criticism is hushed, thoughtful men will read and ponder over the book.

"[14] The book is dedicated by author "to the Mahatma Koot Hoomi whose gracious friendship has given the present writer his title to claim the attention of the European world.

[15][17] 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."

[18] 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...

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.

"[21]On 29 September 1880 during an evening walk with Mrs. Sinnett, Blavatsky, responding to the suddenly expressed desire of her companion to get a little note from one of the "Brothers", tore off a corner of a letter received that day, and held it in her hand until it disappeared.

Mrs. Sinnett pointed to a tree, and then among its branches, she found the same corner of the paper, but now it contained a brief message written in English and signed in Tibetan symbols.

[22][23][24][25]According to Barborka, this note was the first message of the mahatmas, which had come in response to an oral request, and after it Sinnett decided to write his first letter to the "Unknown Brother.

[37][23][38][note 11] "While the letters [from the mahatmas] are the most valuable portion of the book", the most likely cause of its widespread popularity was the occult phenomena described by the author, which he observed personally.

[8][note 12] Guénon wrote that Sinnett, who "at the beginning probably contributed more than anybody else to make Theosophism known in Europe, was genuinely fooled by all of Mme Blavatsky's tricks.

[41] At the end of this section, Hodgson claimed: "I think I am justified in saying that the phenomena relied upon by Mr. Sinnett in The Occult World can be accounted for much more satisfactorily than can the performances of any ordinary professional conjurer by the uninitiated observer, however acute; that the additional details which I have been enabled to furnish in connection with some of the incidents Mr. Sinnett has recorded, clearly show that he has not been in the habit of exercising due caution for the exclusion of trickery; and that he has not proceeded in accordance with those 'scientific modes of investigation' which he explicitly declares (Occult World, p. 35) he regarded as necessary for the task he attempted.

"[44]An American Spiritualist Henry Kiddle addressed in 1883 in a London spiritualist magazine Light letter to the editor,[45] in which he said that after reading Sinnett's book The Occult World, he was "very greatly surprised,"[46] when he discovered that one of Kuthumi's letters published in the book contains text which "was for the most part quite simply the copy of a lecture", which he made at Lake Pleasant 15 August 1880,[47] and published the same month in Banner of Light.

In this connection, Kiddle asked: "As Mr. Sinnett's book did not appear till a considerable time afterwards (about a year, I think), it is certain that I did not quote, consciously or unconsciously, from its pages.

It was dictated mentally in the direction of and precipitated by a young chela not yet expert at this branch of psychic chemistry, and who had to transcribe it from the hardly visible imprint.

Yet had I dictated my letter in the form it now appears in print, it would certainly look suspicious, and however far from what is generally called plagiarism, yet in the absence of any inverted commas it would lay a foundation for censure.