Some years ago I happened upon a homily given by Abp. Joseph Augustine DiNoia on the feast of St. Thomas Aquinas. The subject of his homily was a line from Guillermo de Tocco's biography of Aquinas, in which Thomas is described as "consumed by the holy mysteries" of the eucharist. DiNoia goes on in his delightful voice and typically poignant rhetorical style to give an exposition on the meaning of this phrase, focused on the meaning of "mystery". To this day I remember that homily when I think about the word.
Mystery comes from the greek word μυστήριον, which means "something hidden" or "secret". It is what the word sacramentum translates in Latin. One thinks of the Bacchic mysteries in Euripides, and other similar cults in ancient Greece. Christianity was, in its inception, a mystery religion, i.e. a religion in which initiates were allowed to participate in certain ritual activities prohibited to outsiders. One had to be catechized before being baptized, and one had to be baptized before receiving the eucharist. So it is even today.
But aside from admission to the hidden rites, there is something else characteristic of mystery cults that Christianity shares, and this is the belief is a hidden, higher knowledge that is unavailable to non-initiates. In Catholic theology this latent gnosticism is expressed in several ways. First of all in the notion of the "light of faith" by which the articles of the Catholic faith become intelligible and credible to believers. Second in the tiered platonism of theological knowledge, and the notion that spiritual insight is granted to those who have achieved greater holiness through grace.
One of the corollaries of this gnostic aspect to Catholicism is the conviction that those who reject the faith must do so out of either a failure to understand or an intellectual darkening consequent upon bad moral choices. I can't tell you how many times I have myself said or heard other say that so and so fell away from the faith "in order to justify a sinful lifestyle", or lamented along the lines of Fulton Sheen that “There are not one hundred people in the United States who hate The Catholic Church, but there are millions who hate what they wrongly perceive the Catholic Church to be.”
Sheen's quote unintentionally accentuates the extent to which Catholicism remains a quasi-gnostic mystery cult to the present day. As a student in catholic schools, as a parishioner in various churches, and then later as a CCD and high school theology teacher, one of the things that was consistently impressed upon me was just how many people within the Church "wrongly perceive what the Catholic Church is"—clergy, laymen, educators, and theologians. In fact, for the typical catholic attending a typical parish, going to parochial school or CCD classes, the "actuality" of Catholic orthodoxy is not generally available except in snatches.
To "find Catholicism" one usually has to engage in extracurricular research, and one has to have enough critical ability and intelligence and luck to find the right resources and dig in deep. Even then there is frequently confusion and disagreement, and not just because of the difficulty of the questions but because of the contradictions offered by various legitimate authorities in the Church (the pope, the cardinals, the bishops, the theologians, the clergy generally). The obvious examples are things like the value of ecumenism, the acceptability of Universalism as a theological position, the permissibility of the death penalty, the possibility of women's ordination (an open question? an infallibly settled question?), the nature of mortal sin, the conditions for the validity of various sacraments, and so on.
All this leaves aside the fact that most Catholics do not have the luck or the resources to even consider such theological questions, and, I would say from abundant personal experience, tend to get much more fundamental and non-controversial questions quite wrong. An obvious example here is the very subject of Archbishop DiNoia's homily—the real presence of Christ in the Eucharist, which the majority of American Catholics reject. It makes the Sheen quote somewhat comedic, and invites a parody along the lines of "There are not one hundred people in the United States who believe the true Catholic Faith, but there are millions who reject it in favor of what they wrongly perceive the Catholic Faith to be."
There are, of course traditional responses to this. One is to appeal to the idea of a "smaller and holier" church within the Church, the church of the orthodox faithful who receive the sacraments and so on. And then naturally there's the Vincentian Canon ("Quod semper, quod ubique, quod ab omnibus.") which would seem to offer some sort of norm usable together with a lot of historical research to figure out the truth. But what strikes me as most odd about the Church as a gnostic mystery cult, is how much this state of affairs seems to contradict the core theological/historical vision of Christianity.
The Church teaches that Christ came in order to bear witness to God's saving love for mankind, and that Christianity has always been growing and evangelizing, in order to spread over the face of the whole globe, and communicate the offer of salvation to everyone. But why would the New Vine or the ark of salvation be allowed to fall victim to such crippling error at every level and for so long?
And more to the point, why would a loving God seeking to offer salvation to humanity do so by means of a mystery cult, in which the secret knowledge necessary to avoid eternal hellfire is hidden, imperfectly mediated, frequently modified, and in most cases never communicated at all?
One begins to wonder, after all, at the idea of "public" or "general" revelation. Is there such a thing? Looking around, it seems that Christianity has evolved so far as to make the entire business of finding one's faith a matter of retroactively constructing a tradition in defense of the variant or sect one has chosen today, based on chance and upbringing and psychological dispositions.
And if the latter is the case, and there is no salvation outside the Catholic Church, isn't it rather capricious and unfair of God to have set mankind such a conundrum, and laid out such a punishment for failing to solve it?