After the Great Litany, psalm verses are chanted proper to the particular occasion. These psalm verses are called the antiphons because they were, and sometimes still are sung by the people in two choirs, each responding antiphonally to the other. There are three sets of antiphons at each Divine Liturgy.
Historically the antiphons were chanted by the people in solemn procession to the church where the Divine Liturgy of the day was to be celebrated. Today, although they are now part of the service itself, they still form the joyful preparation for entrance into the worship of Christ through the Word of the Gospel and the offering and receiving of Holy Communion.
The psalms normally sung as the antiphons at the Divine Liturgy of the Lord’s Day are Psalms 103 and 146. On feast days other psalms are used with particular relevance to the special celebration. To these psalm verses, refrains are added proper to the occasion.
Following the second antiphon, a hymn by the Emperor Justinian, Only-begotten Son, is always sung. It is a hymn of faith in the divinity of Christ and his incarnation, crucifixion, and resurrection as “one of the Holy Trinity” for the salvation of men.
In addition to the two sets of antiphons and the singing of Only-begotten Son, which belong to every Divine Liturgy, a third antiphon is chanted which on normal Sundays in most Orthodox Churches is the Beatitudes of Christ’s Sermon on the Mount according to the Gospel of St. Matthew (Mt 5:3-12). The Beatitudes are sung with the refrain taken from the words of the Good Thief on the Cross: Remember us, O Lord, when Thou comest in Thy Kingdom (Lk 23:42). On festal occasions special psalm verses with the singing of the Troparion of the day constitute the third antiphon at the Divine Liturgy.