Only-Begotten Son (Ancient Greek: Ὁ Μονογενὴς Υἱὸς, Church Slavonic: Единородный Сыне, Old Armenian: Միածին Վորդի, English: Only-Begotten Son), sometimes called "Justinian's Hymn", and/or the "Hymn of the Incarnation", was composed around the 4th or 5th centuries. This hymn is chanted at the end of the Second Antiphon during the Divine Liturgies of St John Chrysostom, St Basil the Great and of St Gregory the Illuminator (Armenian Divine Liturgy) .
This hymn is sometimes ascribed to Pope Athanasius I of Alexandria. It was written after the First Ecumenical Council at Nicea as an affirmation of the Christological Formula set down by Athanasius. It was first used in the Church of Alexandria but was distributed by Athanasius to all the churches of the world. It is still currently used as a mournful hymn during the service of Great Friday in the Coptic Orthodox Church of Alexandria, with its length exceeding 10 minutes due to its long and deep melismatic nature. It is also chanted in the introductory portion of the Divine Liturgy of the Eastern Orthodox Church and those Eastern Catholic Churches which observe the Byzantine Rite. The hymn is a theological statement of faith in the dogma of the Incarnation.
There is also a tradition that Emperor Justinian is the person responsible for the hymn's spread and popularity. During the controversy caused by the Origenists, Emperor Justinian declared that this hymn should be sung in all Christian Churches. Due to this tradition, the hymn is sometimes referred to as "Justinian's Hymn".
Only-Begotten Son and Immortal Word of God,
Who for our salvation didst will to be incarnate of the holy Theotokos and Ever-Virgin Mary;
Who without change didst become man and was crucified;
Who art one of the Holy Trinity, glorified with the Father and the Holy Spirit:
O Christ our God, trampling down death by death, save us!
The key word, Monogenes, is drawn from the Gospel of John 1:14, 1:18, and 3:16. The first of these verses describes the pre-incarnate Logos as being "only-begotten of the Father"; the second speaks of Jesus' earthly ministry; and the third describes the offering of the Incarnate Christ for the salvation of those who believe. The term Monogenes is also found in the Nicene Creed as established by the First Ecumenical Council in 325 AD.