“Enq: Can you give me some proofs of its esotericism?
Theo: The best proof you can have of the fact is that every ancient religious, or rather philosophical, cult consisted of an esoteric or secret teaching, and an exoteric (outward public) worship.
Furthermore, it is a well-known fact that the MYSTERIES of the ancients comprised with every nation the “greater” (secret) and “lesser” (public) MYSTERIES – e.g., in the celebrated solemnities called the Eleusinia, in Greece. From the Hierophants of Samothrace, Egypt, and the initiated Brahmins of the India of old, down to the later Hebrew Rabbis, all preserved, for fear of profanation, their real bona fide beliefs secret.
The Jewish Rabbis called their secular religious series the Mercavah (the exterior body), “the vehicle”, or, the covering which contains the hidden soul – i.e., their highest secret knowledge.
Not one of the ancient nations ever imparted through its priests its real philosophical secrets to the masses, but allotted to the latter only the husks.
Northern Buddhism has its “greater” and its “lesser” vehicle, known as the Mahayana, the esoteric, and the Hinayana, the exoteric, Schools. Nor can you blame them for such secrecy; for surely you would not think of feeding your flock of sheep on learned dissertations on botany instead of on grass?
Pythagoras called his Gnosis “the knowledge of things that are”, and preserved that knowledge for his pledged disciples only; for those who could digest such mental food and feel satisfied; and he pledged them to silence secrecy.
Occult alphabets and secret ciphers are the development of the old Egyptian hieratic writings, the secret of which was, in the days of old, in the possession only of the Hierogrammatists, or initiated Egyptian priests.
Ammonius Saccas, as his biographers tell us, bound his pupils by oath not to divulge his higher doctrines except to those who had already been instructed in preliminary knowledge, and who were also bound by a pledge.
Finally, do not we find the same even in early Christianity, among the Gnostics, and even in the teachings of Christ? Did he not speak to the multitudes in parables which had a two-fold meaning, and explain his reasons only to his disciples?
“To you”, he says, “it is given to know the mysteries of the kingdom of heaven; but unto them that are without, all these things are done in parables” (Mark iv. 11).
“The Essenes of Judea and Carmel made similar distinctions, dividing their adherents into neophytes, brethren, and the perfect, or those initiated” (Eclec. Phil.).
Examples might be brought from every country to this effect.”
H. P. Blavatsky
The Mark Of God: Understanding Your "I AM Presence" 