"Esoterica" may refer to things known only to the initiated, a select few. It's specialized knowledge available solely to those who come to be aware of it through means unavailable to most, i.e. to ordinary folk. That's what it refers to in this post, in any case.
Esoterica, for my purposes, includes special knowledge pertaining to things both profane and sacred. It's been a part of Western culture since ancient times; at least such knowledge has been claimed to exist and be possessed by those fortunate few who obtain it. I don't pretend to know much of anything of Eastern culture but suspect esoterica plays a part in it as well, we humans being what we are.
We see it in ancient times in the Eleusinian mysteries and in the mystery religions and cults which flourished during the Roman Empire, where initiation into the mysteries was required to obtain knowledge and salvation. It was necessary that initiates perform or participate in certain ceremonies or rituals. It required in some cases a special kind of learning, astrological learning, for example. Those called the Gnostics pretended to esoteric knowledge, and it was claimed that such as Hermes Trimegistus obtained and wrote of it. It was connected, as may be guessed, with mysticism and magic.
It didn't by any means disappear after Christianity took hold of the Empire, Christianity having its share of esoterica. But Christianity at most inhibited for a time esoterica which may be said to be unrelated to Christian doctrine. From the 17th century on, it seems that esoterica and what may be called esoteric societies have cropped up seemingly as an alternative to Christianity. Those societies still flourish today.
There are of course the Masons. Then there are the Rociscrucians and lesser known societies such as the Ancient Order of Druids, formed in the 18th century. The Knights of Columbus appears to be a kind of freemasonry for Catholics. The Illuminati and the Bilderberg Club are favorites of conspiracy theorists of various kinds.
My favorites are the Ordo Templi Orientis and Hermetic Order of the Golden Dawn. The latter was created in the 19th century, the former in the 20th century. These two even more than others were devoted to the magic arts and ancient pagan gods and goddesses, or at least rituals they imagined were involved in pagan worship. The Ordo Templi Orientis was founded by the very odd Aleister Crowley who, in certain photographs, bears a remarkable resemblance to Uncle Fester of the Adams Family, especially as he appears in the movies. Crowley seems to have worshipped every god at one time or another, though he was partial to ancient Egyptian deities. He claimed to have been contacted by an entity named Aiwass while in Egypt, and with his assistance wrote a book which became the foundation for his religion, called Thelema. It's not surprising that L. Ron Hubbard was influenced by him.
The Order of the Golden Dawn included William Butler Yeats among its members, and seems to have been associated with Crowley as well. It was also devoted to the magic arts (Crowley liked to use the spelling "magik"). Meetings of these societies involved dressing in what were thought to be clothing worn by ancient Egyptian priests. The Egyptian craze resulting from the discovery of Tutankhamen's tomb may have influenced the societies and their members.
It seems that peculiar clothes play an essential part in meetings of these societies, even those more common societies with which we're familiar. The Masons don aprons and other items they imagine were worn by medieval builders. The Knights of Columbus wear special hats, sashes, capes and carry swords, at least when they've attained a special rank.
I wonder what it is that prompts adults to gather together and wear costumes which would otherwise be considered silly, and engage in arcane rituals. I understand that such societies can be a place for what we like now to call "networking" and suppose that if this results in financial or professional success it could well be worth dressing like a fool for an hour or so, especially when everyone else is similarly attired. Is it thought to be a way of carrying on a tradition? An elaborate game of dress-up for adults? Is it thought to impress others, or please the gods or God, or render the wearer more potent in magic or knowledge? Do these societies instill a sense of brotherhood? Do they please the animal in us, these rankings and this hierarchy?
One would think that acquiring esoteric knowledge or power need not be something requiring a gathering of a community appropriately dressed, although the recitation of certain words and the conduct of certain ceremonies would seem to have been required for magic of any kind for a very long time, and throughout our history. Gatherings associated with esoterica would therefore seem to satisfy more of a social impulse than anything else. Perhaps that's a sense of brotherhood or a sense of comfort in the knowledge that others are as we are and want what we want, and willing to do what's being done.
But esoterica and the quest for it seems to be, like so much else of what we do and think, the result of our persistent desire, even need, to control things beyond our control, e.g. such things as death, our fate, others, the world, the universe. Associated with that desire or need is our fear of such things, especially death and the loss of self. This seems to be one, at least, of the bases of our religious instinct.
The Stoic injunction to be undisturbed by things beyond our control strikes me as having a profound effects. Not only does it quiet our fears and concerns and our foolish ambitions, thus making happiness a possibility, but it renders certain all-too-common irrational conduct unnecessary and unreasonable. It isn't necessary to accept complicated rituals and rules or believe in magic or gods to attain happiness and tranquility. Esoterica is irrelevant. We need only exercise control of ourselves.