Daily office

In the practice of Christianity, canonical hours mark the divisions of the day in terms of periods of fixed prayer at regular intervals. A Book of Hours normally contains a version of, or selection from, such prayers.

The practice of daily prayers grew from the Jewish practice of reciting prayers at set times of the day: for example, in the Book of Acts, Peter and John visit the temple for the afternoon prayers (Acts 3:1). Psalm 119:164 states: "Seven times a day I praise you for your righteous laws" (of this, Saint Symeon of Thessaloniki writes that "the times of prayer and the services are seven in number, like the number of gifts of the Spirit, since the holy prayers are from the Spirit").

This practice is believed to have been passed down through the centuries from the Apostles, with different practices developing in different places. As monasticism spread, the practice of specified hours and liturgical formats began to develop and become standardized. Around the year 484, the Greek-Cappadocian monk Sabbas began the process of recording the liturgical practices around Jerusalem while the cathedral and parish rites in the Patriarchate of Constantinople evolved in an entirely different manner; the two were synthesized commencing in the eighth century to yield an office of great complexity. In 525, Benedict of Nursia set out one of the earliest schemes for the recitation of the Psalter at the Office. With the Cluniac reforms of the 11th century there was a new emphasis on liturgy and the canonical hours in the reformed Benedictine priories with the Abbey of Cluny at their head.

...
Wikipedia