This part of the liturgy is so called because in ancient times, during its celebration, catechumens and penitents, of other faiths and even pagans, were allowed to be in the vestibule of the church, and to remain there until the deacon announced their departure.
Since the time of the primacy of the Church, this part has consisted of psalmody, readings of passages from both testaments and prayers for the final confirmation of the catechumens. In a mysterious meaning, it primarily depicts the deeds of the Son of God, done by Him for our salvation, from the time of His incarnation until His suffering. It begins with the memory of His Nativity, namely: the church curtain is taken away from the royal gates, while they still remain closed; - this depicts that only the upper world (represented by the altar), and very few people from the world of the valley, had the opportunity to penetrate the great secret of the fulfillment of the Eternal Council, such as the Prophets and Patriarchs, the Blessed Virgin, Righteous Joseph, etc., and recognized the Son of God in the born Jesus, while others did not recognize the promised Messiah in Him. And therefore, before the beginning of the service of this part of the Liturgy, the priest and deacon, standing before the Holy.
During the meal, they pray reverently, calling on the Comforter-Spirit of Truth, who can cleanse them from all filth, and remembering the Nativity of Christ, they repeat the Angelic song Glory to God in the highest.
Then the deacon, having accepted the priest’s blessing to bring worship to the Lord on behalf of all believers, goes from the altar to the royal doors, and repeats this petition publicly with the words: Bless the Master! By this he depicts the Shepherds who, having sung the glory of God together with the Angels, hastened to Bethlehem to worship the Savior. The priest responds to this exclamation with the words: Blessed is the Kingdom of the Father and the Son and the Holy Spirit, etc. and the clergy, on behalf of all those present, confirms these words with the Hebrew word Amen, which means truly or so be it.
This is followed by the great litany, in which the deacon, having asked for all the blessings and remembering the common and closest Intercessor of all those who pray, the Most Pure Ever-Virgin, commits the fulfillment of the counted petitions and the very lives of those asking into the hands of Christ God.
The priest concludes this prayer with the words: For all glory, honor and worship, etc., are due to You, expressing by them that everything asked of God is asked for the sake of His glory; for to show such love for mankind to sinners and the unworthy is only a deed befitting the Glory of God alone. The clear confirms this with the word: Amen.
After the great litany come the Antiphons, that is, verses whose content is either praise and confession of the name of God, or an explanation of the essence of the holiday being celebrated. They were partly selected from the events of the Old Testament, partly from the Gospel history, in order to make it clearer that the One about whom the Prophets predicted had already appeared in the world. The antiphons are divided into three parts, separated from one another by small litanies.
Before the litany of the second part, the Troparion is sung: The Only Begotten Son and Word of God, which was introduced since the time of the Nestorian heresy, as a dogmatic refutation of the words of this false teacher, who tried to prove that the Mother of God should be called not the Mother of God, but the Mother of Christ.
The words of this troparion depict the moment when, at the baptism of the Lord, a voice was heard from heaven, testifying that this is the beloved Son. One of the Holy Trinity.
At the end of the third part of the Antiphons, there follows an exit with the Holy Gospel, the so-called small exit. It depicts the beginning of the preaching of Jesus Christ; The candle presented to the Gospel depicts both the Forerunner of Christ, John, and the fact that the teaching of the Gospel is the true light, enlightening every person coming into the world. The deacon, stopping at the royal doors, exclaims: Forgive Wisdom! This means that those praying, listening to the action of the Liturgy, would understand in them the hidden wisdom of God in the simplicity of spirit and heart, and without any vain thoughts or pitiful vanity. Excited by these words, those present in the person of the clergy solemnly proclaim: Come, let us worship and fall before Christ. Then troparia are read in honor of the celebrated Saints, depicting that Christ, after His resurrection, opened the doors of heaven to them all.
After this, the priest, having blessed the deacon to perform the Trisagion hymn sung by the Angels, himself begins it with the words: For Holy is our God; The deacon, bringing prayer to God for the believers, in the words Lord! Save the pious, excites them to sing the Angel’s song forever and ever. As a result, those present, having confirmed in the person of the clergy the words of this excitement with the cry of Amen, i.e., let it be, begin to sing: Holy God, adding to these Angelic words, the words of sinful humanity: have mercy on us, as necessary for those who await the mercy of God.
At the end of the Trisagion hymn, the priest ascends to a high place, signifying the heavenly throne of the majesty of God, on which the Son of God, sitting at the right hand of the Father, rules all the worlds; and the deacon shouts out loud! anticipating those praying that the time is coming for reading the Apostolic teaching, inspired by Christ Himself to His chosen ones, whom He sent to preach before His face; and therefore the priest, repeating the words of His covenant about peace (Luke 10:6), turning to those present, proclaims: peace to all! The reader of the Apostle, thanking him on behalf of those present, expresses their desire for the same peace to the soul of the celebrant; and therefore he proclaims to your spirit! After this, the deacon loudly pronounces Wisdom! thereby arousing attentive listening to be read, and the clergy, repeating the words of the reader of the Apostle, sings the Prokeimenon, that is, one of the verses of the psalm, more appropriate to the content of the Apostolic Epistle, and then, after a second exclamation from the deacon: Wisdom! Let's see! — the reading of the Apostle begins.
During it, the deacon burns incense on the altar and on those standing by, thereby expressing the desire that these latter, through the power of unconditional faith in the words of the teaching they listen to, as well as in the words of the Holy Gospel that follows it, become the fragrance of Christ of God. At the end of the reading of the Apostle, the priest teaches peace to the reader, expressing this with the words peace to you, and he, responding with the usual wish and your spirit, excites the clergy to the praise of God by singing Alleluia.
This is followed by the removal from the altar and the reading of the Gospel in front of the royal doors, preceded by the same exclamations of the priest and deacon, with the addition of the words: Forgive us, let us hear the Holy Gospel (that is, with a pure heart). This reading depicts the personal preaching of Jesus Christ, during which He not only taught, but also did good (Acts 10:38), and therefore, both at the beginning of this reading and at the end of it, grateful believers sing: Glory to Thee, Lord, Glory to Thee! With the end of the reading of the Gospel, the priest descends from the high place and, having received the Gospel at the royal doors, goes with it to the throne; the deacon, remaining at the place of reading, begins to pronounce a special litany.
At the end of this litany, the removal of the catechumens follows, because the time for the gifts is approaching, at which they are not yet worthy to be present; but before their departure, they are commanded to finally, this time, turn with a prayer for themselves to the Lord, and for this the deacon proclaims: Pray the catechumen of the Lord for yourself! and at the same time, believers are invited to join their prayers to theirs so that the Lord may have mercy on them; announced them with the word of truth and joined them to his Catholic and Apostolic Church. At the end of this prayer, the deacon, commanding the catechumens to bow their heads before the Lord to receive a blessing from Him, announces to them the time of their removal from the church, proclaiming: Depart from the catechumens!
This presentation of the catechumens from the church, according to Simeon of Thessalonites, depicts the end of the world, when, according to the saying of the Savior Himself, the Gospel of the Kingdom will be preached throughout the entire universe as a testimony to all nations - and then the end will come (Matthew 24:14). Then He will sit on the throne of His glory; and all nations will be gathered before Him, and He will separate them from one another, just as a shepherd separates the sheep from the goats (Matthew 25:31-33).
Therefore, the Church, after the Gospel, commands the catechumens to leave the church, leaving only the faithful in it.