By Archimandrite Epiphanios Theodoropoulos
On Great Thursday we perform the commemoration of four events: a) the washing of the feet of the apostles by the Lord, b) the Secret Supper, namely the Lord's deliverance to us of the Mystery of the Divine Eucharist, c) the wondrous prayer of the Lord to His Father, and d) the betrayal of the Lord by Judas.
To these events are the hymns of the day dedicated. First the troparion "When the glorious disciples" is chanted. After the Gospel (Lk. 12:1-39) and the 50th Psalm, there follows the complete Canon with the acrostic: "On Great Thursday I chant a great hymn." This Canon begins with the Irmos "The Red Sea was cut by a rod." Between the the 3rd and 4th Ode there is inserted three Kathismata. After the Canon the Exaposteilarion "I see Your bridal chamber" is chanted, then the Stichera Idiomela of the Praises and the Aposticha. Before the Dismissal there is a reading from the book of the Prophet Jeremiah (11:18-23; 12:1-5, 9-11, 14-15).
Great Thursday is the day of the deliverance of the Mystery of the Divine Eucharist and because of this Vespers today is wedded to the Divine Liturgy of Basil the Great. This Liturgy is performed in the morning hours, because in the evening is performed the Matins of Great Friday.
Source: Η Μεγάλη Εβδομάς μετά ερμηνείας, 9η έκδ. Αθήνα, Αποστολική Διακονία της Εκκλησίας της Ελλάδος, 2002. Translated by John Sanidopoulos.