On August 15, Orthodox Christians celebrate the greatest of all the religious festivals which the Church established in honor of the All-Holy Virgin Mary (Panagia), the feast of the Dormition (Koimêsis) of the Theotokos.
The feasts of the Virgin Mary (theomêtorikai eortai) are second in importance after those of our Lord Jesus Christ in the annual cycle of festivals observed by the Orthodox Church because, after our Lord Himself, the All-Holy Virgin is the most blessed person in our Church.
If the Lord’s greatest Feast is that of Pascha, the Feast of His redemptive Death and Resurrection, then His Mother’s greatest feast is also associated with her death and metastasis (i.e., translation or transposition) to Heaven. The reason for this is to be found in the basic Christian perception of salvation, which is none other than the reentry of human beings into God’s eternal kingdom, transcending death and regaining the gift of eternal life.
In our Orthodox tradition, the blessed person of the Theotokos is inseparable from the blessed person of our Lord and Savior Jesus Christ. This is exactly what the name, Theotokos (i.e., the God-bearer, Mother of God) constantly declares: namely that the place and significance of the Virgin Mary in the Church cannot be understood apart from her relation to our Lord.
What is declared by the name Theotokos is most tangibly depicted on the iconostasion (the icon screen before the sanctuary) of any Orthodox Church. The icon of the Lord’s is always on the right of the Beautiful Gate, and the icon of the Theotokos is always on the left. This particular icon, depicting the All-Holy Virgin Mary holding our Lord and Savior as a child in her arms, is the most characteristic of all icons associated with her blessed person.
The hymns of this feast, which are among the most significant of the Orthodox liturgical year, bring out not only this basic Christian perception of salvation but also the important place that the blessed person of the All-Holy Theotokos has in this perspective.
The Feast of the Dormition was established in the 6th century, although its roots go back to earlier centuries, especially the 5th century, following the dogmatic decision of the 3rd Ecumenical Council of Ephesus (431) to accept and use the term, Theotokos as the most important and defining description of the All-Holy Mother of our Lord in the Church.
According to Dr. Ioannis Fountoulis, Professor of Liturgics at the University of Thessaloniki, this feast was joined to an earlier feast in honor of the Theotokos at the famous church of the All-Holy Virgin Mary in Gethsemane, which had been erected by the Byzantine Emperor Maurice over her tomb.
The details of the celebration of the feast of the Dormition, especially those revealed in its hymns, are based on an apocryphal narrative concerning the circumstances of the death of the Theotokos, which goes back to Saint John the Theologian, the beloved disciple of the Lord in whose care the All-Holy Theotokos had been entrusted.
The narrative tells us the story, which is beautifully depicted on the holy icon of the Dormition. It tells us that the All-Holy Theotokos was visited by the Archangel Gabriel and foretold about her approaching death; that thereupon the Theotokos returned to her home and prepared for this event, praying at the same time that the Apostles should be notified accordingly. John is said to be the first to arrive in a miraculous way, and then all the rest follow. Finally, the Lord Himself appears in His dazzling divine glory, escorted by a myriad of angels, and takes her all-holy soul, which is wrapped up like a newborn babe in swaddling clothes, into His arms in order to transport it to Heaven.
~By Protopresbyter Dr. George Dion Dragas, taken from Mystagogy: The Weblog of John Sanidopoulos (http://www.johnsanidopoulos.com/2010/08/dormition-of-theotkos.html