The esoteric/exoteric distinction
The word esoteric possesses a certain mystique to the untrained ear, but has a technical meaning in the study of religions – an esoteric religion is one in which different things are taught to adherents at different levels of the faith.
For example, scholars of Buddhism in the past tended to trace two main streams of Buddhism – Hinayana (smaller vehicle) and Mahayana (greater vehicle), with Hinayana gaining prominence in southeast Asia, and Mahayana Buddhism enjoying much greater purchase in regions like Tibet, China, Korea, and Japan. As you can probably guess, scholars of the Mahayana school originally coined the term "smaller vehicle" for their religious compatriots (who would willingly choose such a diminutive name?), but while today the use of the term Hinayana to describe any Buddhist group is discouraged, the two streams do still roughly map to this distinction between exoteric and esoteric teaching.
The teachings found in predominantly exoteric streams of Buddhism focus on the idea of accruing karma through right action in order to move up the ladder of beings, so to speak, until one can reincarnate as a Buddha capable of attaining enlightenment. Samsara is this realm of suffering which we inhabit, and in which we die and re-incarnate on the basis of our karma. Exoteric traditions tend to place a greater focus on specific rituals and ascetic practices than Mahayana traditions, and also are more likely to include an elaborate pantheon of cosmic beings who can be entreated for aid on one's journey through samsara on the way towards enlightenment.
Mahayana traces its lineage from the more philosophical schools in India whose thought found a natural resonance with indigenous traditions of metaphysical reflection already present in Tibet and China at the time of Buddhism's arrival. This esoteric Buddhism which flourished in eastern Asia emphasizes that the stories about karma, samsara, boddhisattvas, and the like are a "skillful means" which are sufficient for a beginner to start their journey towards enlightenment, but which must be surpassed in order to awaken to the truth. Awakening consists in realizing the fundamental emptiness of all things, including the very means by which one came to this realization. In short, one must kick the ladder away after they have climbed up.
Christianity as a historical religion
I commented in a Twitter thread the other day that the Christian Church has not historically admitted any such distinction between what is taught and what is believed. Unlike Buddhism, which employs the doctrine of skillful means, Christianity doesn't offer tiers of instruction where the prior level's teachings must be discarded in the ascent to the next in the sequence towards the ultimate hidden truth only propagated amongst an inner circle of the most dedicated. The Gospel – the good news of Jesus Christ -- is the same for every man, woman, and child. In fact, this was a crucial dividing line between early Christian communities and rival Gnostic communities which publicly said one thing but demanded people be initiated into the group in order to learn the true nature of their teachings.
Christianity doesn't have this exoteric/esoteric distinction because it differs from other religions in that it purports to offer a report about particular historical events, not primarily a morality, a mythos, or a metaphysics. Certainly Jesus gives us ethical commands, and certainly if the good news of Jesus is true it has certain consequences for how one might do metaphysics, but the central message which Christianity propagates is the news of the historical event of Jesus Christ's life, death, and resurrection. Everything else flows from that event as a consequent.
Consider that most Buddhists don't quibble with each other about the historical reality of any particular Buddha or cosmic entity described in any of the prominent sutras. There isn't even an established canon of texts which the majority of Buddhists ascribe any sort of authority to, much less an authority which is derived from a theory of divine inspiration or the like. Meanwhile, Christians have interminable debates about who the author of Hebrews was. I contend that this is actually a feature of Christianity, not a bug. The only problem is when such debates get in the way of, rather than serve, the main priority – spreading the good news about the work of Jesus, the son of God, who was crucified and resurrected in Palestine sometime in the early part of the first century. Thus, Christianity cuts against the exoteric/esoteric distinction because it has historically viewed the canon of Scripture as a collection of texts written by eyewitnesses to God's actions in history, not philosophical treatises based on private metaphysical speculation.
Mystical readings and mystical experiences
Having said all of this though, honesty compels me to take a moment to provide some nuance, all with the goal of diving deeper into the phenomenon at hand.
While I still want to emphasize the fundamental importance of what I've said about Christianity's nature as a historical religion meaning that it doesn't sustain an exoteric/esoteric distinction in its teaching, it's nonetheless the case that we can identify exoteric and esoteric threads running through the history of the Church. In fact, there are two phenomena which I think are specifically worth mentioning – (1) the "anagogical" sense of reading in the Four Senses of Scripture, and (2) private mystical experiences of individual Christians. There are two other interesting examples which I think are worthy of being treated in their own individual posts, but I will forestall discussing those for now, and will update this essay with links once I write those pieces.
Since early Christianity was functionally a heretical sect of Judaism which grew by welcoming Gentiles into God's family, Christians also inherited the allegorical and mystical reading practices of Hellenistic Jews like Philo. Unlike modern hermeneutical theory, readers of texts at the time were comfortable with the idea that a text could be multivalent, and thus be read with different layers of meaning which could be present concurrently in the text without being contradictory. This practice of multivalent reading became called, at least within the Christian tradition, the "four senses of Scripture." In particular, one of the senses came to be called the "anagogical" or "mystical" sense of the text.
The anagogical sense of Scripture maintains that speech about particular events or persons need not have its meaning restricted merely to their corresponding historical particularities, but that these specific events or persons could possess a symbolic function pointing us beyond them to a spiritual meaning. This interpretation doesn't destroy their particularity, but rather uses the particulars as a signpost to a more abstract insight. For example, when the Old Testament prophets speak about the historical people of Israel as God's bride, their speech can lead us to a deeper realization of the Church's mystical union with God in love. These interpretations are not mutually exclusive, as we can read the Prophets in their historical context as marginal figures speaking rebukes and blessings to Israelites, but we can see how their visions and prophecies can also reveal a deeper spiritual reality about what God was doing in Christ and is doing today through His people, the Church.
The question of anagogical interpretations of Scripture leads us directly to the mystical experiences of past Christians, as well as their records of those experiences. We have examples of these experiences in Scripture, such as Isaiah experiencing the holy of holies in Isaiah 7 or St. John on the island of Patmos witnessing the visions recorded in the book of Revelation. However, we also have records of mystical experiences by all kinds of people – leaders of the church, martyrs, nuns, monks, lay people, etc... Every age of the church has seen diverse groups of people experiencing an extreme closeness to God which comes to them usually through intense prayer or fasting or persecution.
Gregory of Nyssa's Life of Moses provides an example which unites the two phenomena we've been discussing – anagogical interpretation and mystical experiences. Nyssa's text is both an attempt to exegete the book of Exodus which describes the story of how Moses leads the people of Israel out of Egypt, but the work climaxes with Moses' ascent up into the dark thunderclouds of Mt. Sinai, which Nyssa uses as a way to explore the soul's mystical ascent to God. He describes how Moses crawls through the darkness searching for God at the top of the mountain, comparing this to how the soul must abandon the physical senses in order to approach God by groping in the dark. It took the ascension of the mountain, the leaving behind of the people, and even the total overwhelm of his senses in order for Moses to directly approach God.
It's no secret that the mystical experiences described by the individuals who encounter them tend to lead us to the outer edges of orthodoxy, even dancing around the boundaries in ways that might made ordinary church leaders uneasy. I mentioned Gregory of Nyssa in the preceding section, and it's worth nothing that he is still looked at askance even today. These mystical experiences by their very nature lay bare both the immense fullness and the profound emptiness of the categories which we rely on in our day to day navigation of our world. Many folks who have private mystical experiences are left with impressions about the emptiness of certain doctrinal disputes or find themselves drained of passion for maintaining certain distinctions which church leaders might zealously prioritize. Some might privately dabble with formal heresies or nurse in their hearts desires or hopes which seem to contradict the direct teaching of Scripture, such as Barth's "hopeful universalism" in which he claims that one cannot teach universalism but that one may nonetheless hope for it in resonance with the clear trajectory of God's reconciling work in Christ.
You might be surprised that even after saying all this I still maintain that the Church has one message, one witness, and one mission, and not two (or more) messages for two classes of people. The labor of the scholar, the mystic, or the minister all happens in the same Spirit and to the same end as the work of any other member of Christ's Body. The reality of heresy of the heart, the overwhelming power of mystical experiences, or simply the nuance of a personal relationship with the God of the universe aren't things which ultimately can be avoided in the people of God, in my opinion. However, I think that Christianity has historically navigated this distinction between private interpretation and public confession by resolving it at the level of practical action.
Lex orandi, Lex credendi – "the law of prayer is the law of belief" — provides a unifying and organizing principle for Christian practice. Can two people come together to pray? This requires a spirit which discerns a fellow traveler, a comrade with whom one shares the Spirit of God. For the one who has had a mystical experience and for the one who has not, the inner mess of beliefs and passions are superseded at the level of practical action – pray the prayers, chant the liturgy, eat the Eucharist, love God, and love your neighbor as yourself. Be in union with your brothers and sisters rather than seeking division and discord. Love the family of God above even your race and your nation. These are the revolutionary activities through which the Kingdom of God comes and in which God's work is manifest.
"“Teacher,” said John, “we saw someone driving out demons in your name and we told him to stop, because he was not one of us.”
“Do not stop him,” Jesus said. “For no one who does a miracle in my name can in the next moment say anything bad about me, for whoever is not against us is for us. Truly I tell you, anyone who gives you a cup of water in my name because you belong to the Messiah will certainly not lose their reward." – Mark 9:39-41