holy immortal,
Have mercy upon us.[31]

An evening hymn, {Phos hilaron}, Joyful light, is mentioned by Basil in
the fourth century as very old. It was sung at vespers in the Eastern
Church:[32]

O gladsome light, O grace
Of God the Father's face.[33]

Among ancient liturgical hymns the _Te deum_ should be mentioned. It is
attributed to Nicetas, Bishop of Remesiana in Dacia, and dated from the
end of the fourth century. It appears to be a combination of three
distinct parts. The first thirteen verses, or parts one and two, probably
originated earlier than the fourth century and may have been inspired by
Cyprian, Bishop of Carthage, 200-258, who wrote in terms almost identical
with the phrases of this early section, used of prophets, apostles and
martyrs.[34]

Biblical sources, especially the canticles, now appear as liturgical
hymns, either in their original form or in an enlarged version.[35] The
use of canticles, more particularly in their variations, is of supreme
interest to the hymnologist, because it offers a theory of the origin of
Christian hymnody apart from liturgical interpolations or from the
psalms. Clement of Rome urged the Corinthians to unite in the spirit of
praise as expressed in the seraphic chorus of Isaiah's vision,

Holy, holy, holy is the Lord of Hosts:
the whole earth is full of his glory,

associating it with the praise of the angelic ministrants, "ten thousand
times ten thousand," beheld by Daniel (_Dan. 7:10_). The same hymn had
been heard in the apocalyptic mysteries of the _Book of Revelation_. Very
early it was incorporated in the liturgy of the eucharist, continuing an
ageless form of the praise of God from the old dispensation into the new.

The evolution of the Great Doxology from the words of the angelic song,

Glory to God in the highest,

to the _Gloria in excelsis_ illustrates the expanding thought of the
Church, corresponding to the growth of the Christian body within the
culture of the Roman Empire. Again, the _Gloria_ illustrates Hellenistic
features of poetic style, bespeaking the oriental influences which had
entered into Greek literature.[36] Note the repetition of the clauses,

We praise thee, we bless thee, we worship thee, we glorify thee, we
give thanks to thee for thy great glory,

of the invocation,

O Lord God, heavenly King, God the Father almighty,
O Lord, the only-begotten Son, Jesus Christ;
O Lord God,