What form did the public prayers, which we may call the divine office,
take in the time of the Apostles? It is impossible to say. But it is
certain 10 that there were public prayers, 20 that they were offered up
daily in certain determined places and at fixed hours, 30 that these
public prayers consisted principally of the Psalms, hymns, canticles,
extracts from Sacred Scripture, the Lord's Prayer, and probably the
Creed, 40 that these public prayers varied in duration according to the
will of the bishop or master who presided.

"The weekly commemoration of Christ's resurrection, the yearly
recurrence of the memory of the great facts of Christ's life, the daily
sanctification of the hours of the day, each led the Christian to draw
upon the hours of the Psalter, and when, gradually, fixed hours for
daily prayer passed beyond the home circle and with groups of ascetics
entered the public churches, it was from the Psalter that the songs of
praise were drawn, and from the Psalms were added a series of canticles,
taken from the books of the Old and the New Testaments, and thus, long
ages before any stereotyped arrangement of the Psalms existed, assigning
particular Psalms to particular days or hours, the Psalms were feeding
the piety of the faithful and teaching men to pray" (_The New
Psalter_--Burton and Myers). In this matter of public prayer, it is
hard for us to realise the "bookless" condition of the early Christians
and their difficulties. It was twenty-five years after the Ascension
before the first books of the New Testament were written, and many years
must have elapsed before their wide diffusion; hence, in their bookless
and guideless condition the early Christians were advised to use the
Psalms in their new devotional life (Ephes. v. 19; Col. iii. 16; St.
James, v. 13).