Christianity does not present us with any formal esoterism in the primary sense of being related to its central mysteries, namely Christ or even the Virgin Mary. What is presented is what it is, and is esoteric for esoterists and exoteric for exoterists. The same goes for the sacraments, which we could say are initiatic for esoterists and salvific for exoterists.
Some have argued to the contrary, pointing usually to the development of Alchemy in the Middle Ages, and the tradition of Hermeticism in general. Likewise, it goes without saying that liturgical calendar could not have been developed without a scientific knowledge of the significance of the seasons, months, days, of the year, and this would correspond to a kind of esoteric science like the others mentioned, something similar in many respects to astrology properly understood and practiced (which is to say, not involving divination).
There is an important distinction, however, between these two orders of esoterism, so much so that we can term the second type (alchemy, astrology, etc.) as secondary sciences. Acknowledging them as such we can fully admit that they do constitute formal esoterisms within the Christian world, with their own formulations and intricate systems of symbolism and practical methods.
This distinction is further justified by the fact that anyone with a certain rational aptitude can become competent in one of these secondary sciences, provided they have access to the keys of proper instruction. Here we can speak of an ‘initiation’ in the sense of a secret knowledge being conveyed by teaching only to those who have business practicing the art. But the central mysteries of the faith—those relating to Christ—there is nothing of the kind, since the ‘esoterism’ in question here does not depend in the least on erudition or the rational powers of the scientist, even if the science is a sacred one, like that of astrology. What the ‘estoeric knowledge of Christ’ requires is a spiritual adeptness, and this may occur in one who is relatively simple-minded, in the sense meant by Christ when he says that only those who become children may enter the Kingdom of Heaven.
So again, we are dealing with the essential or primary esoterism of the Christian faith, which is accessible to anyone and is implicit in the doctrines openly proclaimed to all, but which is realized only in the few, and here we say that Christianity contains no formal esoterism; and then we find a number of secondary esoterisms, succeptible to exclusive transmission and sometimes developed in relative secrecy, and dependent more on a mental qualification than a spiritual one properly speaking, even though it must of course be granted that the object is always spiritual knowledge in all cases.
It was necessary to dwell on this point so that we can situate alchemy and astrology in their properly places within the hierarchy of spiritual truth contained in the Christian revelation: we wish to admit their validity and their value, without attributing to them a kind of preeminence as if obscurity were the criteria of doctrinal value.