Kanon Pokajanen

Kanon Pokajanen is a 1997 composition by Arvo Pärt for four-part (SATB) choir. The text is the "Canon of Repentance to Our Lord Jesus Christ", an Orthodox hymn. The text is sung in Church Slavonic and following the tradition of Russian sacred choral music, it is sung a cappella.
Background.
Arvo Pärt describes his encounter with the text and the history of setting this text to music thus:
He was commissioned by KölnMusic GmbH to write a work commemorating the 750th anniversary of the building of Cologne Cathedral. He finished it in 1997 and it premiered at Cologne Cathedral on March 17, 1998, performed by the Estonian Philharmonic Chamber Choir under the direction of Tõnu Kaljuste, to whom (both choir and conductor) this piece was dedicated.
Structure.
As Pärt said, "the words are very important to me, they define the music" and furthermore "the construction of the music is based on the construction of the text." So the structure of the music is going to be based on its text, namely the "Canon of Repentance."
The Eastern Orthodox canon, in general, is composed of nine odes (though in practice usually only eight are chanted). Each ode begins with an introductory verse called the "eirmos" (pl. "eirmoi") which is followed by four verses called "troparia" (sing. "troparion") all interspersed with antiphonal responses suited for the canon's subject. The last "troparion" is referred to as the "Theotokion", so-called because it is written in honor of the Theotokos (Mother of God).
There are also intermezzo hymns which serve to encapsulate the canon's theme: the "Sedalen" (appears in between Ode III and Ode IV), the "Kontakion" and its "Ikos" (both in between Ode VI and Ode VII), and the Prayer after the Canon (after Ode IX). The latter concludes the canon and can serve as pre-Communion prayer.
The "eirmos" (Greek for "model" or "chain") is a paraphrase of one of the nine canticles found in Scripture, usually taking a specific verse or the general idea in the Biblical song. Here are the list of the Biblical canticles with their traditional names:
Normally the second ode is omitted owing to its severe nature. The most notable exception to this is in the Great Penitential Canon of St. Andrew of Crete which is chanted during Great Lent. In most canons, including the present one, there is no text written for Ode II and therefore there is not an Ode II in "Kanon Pokajanen". The numbering, however, does not change as shown in the outline below for the entire piece:
Musical Characteristics.
"Kanon Pokajanen" exhibits characteristics of Pärt's tinntinabular style. The piece remains almost exclusively in D minor, deviating only in particularly expressive passages and sometimes final cadences (e.g. the piece ends with a Picardy third on D).
Overall, the melodies and harmonies remain fairly static throughout the piece. Variation is created through alteration of the dispositions and roles of the various voice parts. The odes build toward each intermezzo section, treating it as a small climax. The Prayer after the Canon is the most intense of all the climaxes, paralleling the prayer's function.