Between 1880 and 1884, A. P. Sinnett received scores of letters purportedly from the mahatmas Koot Hoomi and Morya, the basis of The Occult World (1881) and Esoteric Buddhism (1883). The originals survive in the British Library; the 1885 Hodgson Report of the Society for Psychical Research concluded they were produced by Blavatsky. Guy and Edna Ballard's I AM Activity (Unveiled Mysteries, 1934) retooled the masters into an American movement around Saint Germain.
New Age culture absorbed the masters as generic 'ascended' teachers, stripped of the Himalayan geography and Victorian letter-delivery logistics. The concept now floats free of its source texts, a brand of authority that requires no institution and answers no questions.
The masters are the esoteric answer to a secular anxiety: someone must be in charge. The Great White Brotherhood is a civil service of the unseen, and the model of hidden adepts steering events is one of the most exportable ideas Theosophy ever shipped.
If the masters only ever arrive as handwriting, what exactly is being worshipped?