Question: "What are we to make of parts of the Liturgy that seem to be relics from a time when the Liturgy was closed to the general public? For example: the dismissal of the catechumens: "Catechumens, depart!" "The doors! The doors!" (usually interpreted as 'close and guard the doors'). In the prayers for Communion, "I will not speak of thy Mystery to Thine enemies." I don't like the idea that these phrases are just fossils. How do we understand them today?"
The practice of dismissing the catechumens generally came to an end in the general life of the Church because most countries in which Christianity existed were almost entirely Christian, and adult converts became a rarity.
There was also a closely related penitential system, that consisted of four groups of people who were guilty of serious sins, and who had been placed under a penance for some period of time: (1) the weepers, who remained outside the church doors and asked prayers of the faithful as these passed into the church; (2) the hearers, who stood in the Narthex of the church behind the catechumens, and were dismissed with the catechumens; (3) the kneelers were allowed into the back of the Nave, but who also were also dismissed with the catechumens; and (4) the co-standers, who were allowed to stand with the faithful in the Nave and attend the entire liturgy, but not receive communion, until they were finally readmitted into communion.
The penitential system eventually came to an end as well. In the early Church, to even join the Church was an act of courage, and thus the level of commitment among the average Christian was very high, and so you could impose strict penitential discipline that might extend for decades, without it being a cause for final despair and apostasy. As time went on, such strict discipline was stronger medicine than later generations of Christians were able to benefit from.
As a result of both of these developments, instead of non-Christians being completely prevented from entering the Church, and catechumens and certain penitents being prevented from entering beyond the Narthex, the Altar area (the area behind the Iconostasis) became the one area that such people were not permitted to enter. This is true at least in general parish practice; however, in some monasteries catechumens and the heterodox are still not allowed into the Nave, and are still dismissed at the time of the dismissal of the catechumens... and so this practice, while no longer common, is actually not entirely a thing of the past.
What does the Dismissal of the Catechumens Mean for the Faithful
The dismissal of the catechumens happens after the Gospel reading, and according to the ancient practice, also after the sermon.
St. Symeon of Thessalonica says that the dismissal of the catechumens represents "the separation of the sinners from the just after the preaching of the Gospel at the end of the ages. For after the Gospel has been preached in all the world as a witness to all peoples, scripture says, "Then the end will come" (St. Symeon of Thessalonika: The Liturgical Commentaries, trans. Steven Hawkes-Teeples, (Toronto: Pontifical Institute of Mediaeval Studies, 2011), p 249).
So the point being that this dismissal should be a warning to us that the time we have to obey the Gospel message is limited, and that the day will come when we will have to give an account, and will either be taken away with the sinners, or receive the reward of the righteous.
Fr. Seraphim Slobodskoy similarly says that the dismissal of the catechumens "should also be a warning to us... We, the baptized, sin frequently and often without repentance are present in the church, lacking the requisite preparation and having in our hearts hostility and envy against our fellow men. Therefore, with the solemn and threatening words, "catechumens depart," we as unworthy ones should examine ourselves closely and ponder our unworthiness, asking forgiveness from our personal enemies, often imagined, and ask the Lord God for the forgiveness of our sins with the firm resolve to do better" (The Law of God: For Study at Home and School (Jordanville, NY: Holy Trinity Monastery, 1994), p. 566).
"For I will not speak of Thy Mystery to Thine enemies..."
In the early Church, there was a high degree of secrecy. This was not at like the Gnostics, who had secrets that were kept even from their own members, and retained by only a select group. Christians did, however, keep many things secret from those outside of the Church. In St. Cyril of Jerusalem's catechetical lectures, he admonished his hearers to not write down what he taught them. As we have already noted, even catechumens were not allowed to remain in the Church during the Eucharistic portion of the liturgy. But what does this prayer mean to us today, when non-Christians can attend a liturgy in its entirety, and when books about the mysteries can be read by anyone who is interested that describe the sacraments in great detail? Fr, Michael Pomazansky addresses this question in his "Orthodox Dogmatic Theology":
"This strictness with regard to the revelation of the Christian Mysteries (Sacraments) to outsiders is no longer preserved to such a degree in the Orthodox Church. The exclamation, "Catechumens depart!" before the Liturgy of the Faithful is still proclaimed, it is true, but hardly anywhere in the Orthodox world are catechumens or the non-Orthodox actually told to leave the church at this time. (In some churches they are only asked to stand in the back part of the church, in the narthex, but can still observe the service). The full point of such an action is lost in our times, when all the "secrets" of the Christian Mysteries are readily available to anyone who can read, and the text of St. Cyril's Catechetical Lectures has been published in many languages and editions. However, the great reverence which the ancient Church showed for the Christian Mysteries, carefully preserving them from the gaze of those who were merely curious, or those who, being outside the Church and uncommitted to Christianity, might easily misunderstand or mistrust them — is still kept by Orthodox Christians today who are serious about their faith. Even today we are not to "cast our pearls before swine" — to speak much of the Mysteries of the Orthodox Faith to those who are merely curious about them but do not to seek to join themselves to the Church." (Orthodox Dogmatic Theology, trans. Fr. Serpahim (Rose), (Platina, CA: St. Herman Press, 1984, p. 31, footnote 12, emphasis added).Exactly where the line should be drawn, and when exactly we are in danger of casting the pearls of our Faith before swine (Matthew 7:6) is not something for which one can lay out simply rules, but this is something that we should pray that God will give us wisdom to discern when dealing with those who are not Orthodox.