"Ye who are about to cross the threshold of the house of God, leave the confusion of your cares behind,
so that within you may find the Judge benign" (St. Theodore of Studion)

St. Nilus came from Byzantine Calabria, whose bishops were under the authority of the Patriarch of Constantinople, and the ritual he brought to Grottaferrata, in the metropolitan territory of the Pope of Rome, was the one followed in the churches and monasteries of his homeland. In 1004, the year when the Abbey was founded, the Churches of Rome and Constantinople were still in perfect communion, though they followed different rites. Fifty years later, the Great Schism divided the Roman Catholic and the Orthodox Churches. The monastery founded by St. Nilus retained its Byzantine rite and traditions, but remained faithful to the Church of Rome. Accordingly, any Catholic can take part in its ceremonies and receive its sacraments.

The liturgy in use at the Grottaferrata monastery is rooted in the Constantinople liturgy established in southern Italy when the region was ruled by the Byzantines. Here the liturgy took on certain features of its own, and thus came to be called Italo-Byzantine: an Italian variant of the Byzantine.

The Divine Liturgy (Holy Mass) celebrated at the Abbey generally follows the formulary attributed to St. John Chrysostom, one of the Fathers of the Eastern Church (d. 407). However, on Sundays during Lent and on certain other solemn holidays, the celebration follows the formulary attributed to St. Basil the Great, archbishop of Cesarea in Cappadocia (d. 379). The Eucharist is distributed in its two parts, wine and leavened bread, according to the account given in St. John's Gospel. St. John says the Last Supper was held the evening before the Jewish Passover, so the participants would have been eating leavened bread as usual, not the unleavened bread prescribed for Passover (the other three Evangelists place the Last Supper on the first night of Passover).

Baptism is administered via triple immersion in the baptismal font. During the ceremony, the infant also receives the sacraments of First Communion and Confirmation.

Weddings are particularly suggestive. The priest welcomes the future spouses at the church door and questions them to make sure that they intend of their own free will to be joined in matrimony. This short interview is an abridgement of the ancient rite of engagement that used to precede the wedding day. After the Divine Liturgy, the wedding ceremony begins. The bride and groom promise to take each other in matrimony, and the priest slips on each one’s fourth finger the ring that symbolizes God’s act of joining them.

Next comes the coronation: crowns are placed on the newlyweds' heads to signify that each receives the other as a crown, at once a splendid ornament and the perfection of oneself. Both then drink blessed wine from the same glass, in memory of the benediction imparted by Jesus at the wedding in Cana. Finally, they walk three times around the altar, each bearing a candle, the metaphor of the conjugal life they are to live together, illuminated by the light of faith.

A typical feature of Byzantine churches is the iconostasis, a partition adorned with icons that separates the nave (where the congregation gathers) from the apse area (the sanctuary, or Vima), where the priests and deacons celebrate the Divine Liturgy at the altar. Three doorways open in the iconostasis. The central one, with double doors, is called the "royal" entrance and is reserved for priests; the side ones are for deacons. Behind the iconostasis, at the center of the sanctuary, is the square altar. Suspended above the altar is a silver dove with outspread wings that serves as a tabernacle; it contains a small piece of consecrated bread. Two small tables stand at the sides of the Vima; the bread of the Eucharist is prepared on one, and ceremonial objects are set on the other.

The priest's liturgical vestments include a colored tunic (stichàrion), a band embroidered with seven crosses (epitrachìlion), two cuffs (epimanìkia) to fasten the ends of the tunic sleeves, and a large mantle (phelònion). The deacon wears a long stole wrapped around his body (oràrion), as well as the stichàrion and the epimanìkia. In solemn ceremonies, the Exarchic Archimandrite of Grottaferrata wears the Byzantine miter and carries the crosier on which two snakes face each other ("Be as prudent as snakes" Matthew 10.16), and the epigonàtion, a small diamond-shaped purse hanging from his belt.

The ritual followed by the Basilian Monks of Grottaferrata is officiated in both Greek and Italian languages, and uses a rich symbolic language: frequent use of the censer, signs of the cross whenever the three Persons of the Holy Trinity are named, and deep bows (metànie) accompanied by the sign of the cross, as manifestations of veneration and penitence.

In the gesture of benediction, the priest presses his thumb against his ring finger, extends his index finger and bends his other two fingers slightly inward, thus representing the Greek letters IC XC, an abbreviation of the name of Jesus Christ. In making the sign of the cross, the thumb and the index and middle fingers are joined together and the hand is raised first to the forehead, next to the chest, then to the right shoulder and lastly to the left shoulder.

A cappella singing is an essential part of Byzantine liturgy; it is considered the best way to express praise of the Divine, an instrument that elevates the soul to contemplation. In Grottaferrata, composing liturgical music (melurgy) is a tradition that goes back to the Founding Saints, Nilus and Bartholomew: a thousand years without interruption. The texts and the melodies of the hymns, whether handed down from ancient manuscripts or composed in recent times, communicate the austere beauty and mysticism of an art that captivates the worshippers and prepares their heart for the Sacred Mysteries.