In the earliest days of the Church, Christian faithful gathered (or were required to gather) twice a day, in the evening and in the morning to sing hymns and psalms, and to hear the scripture and teachings. These meetings (called *synaxeis, *sg. synaxis) later developed into Vespers and Matins, and were practised widely and developed mostly in parish settings until the end of the Middle Ages. The other hours developed in response to the admonition in Ps 118 (or Proverbs) that the just man prays seven times a day, giving rise to psalmody at 9:00 AM, Noon, 3:00 PM, before retiring to bed, and at midnight (later a service at 7:00 AM was added, but this was in response to monks going to sleep between Lauds-at 6:00 AM-and the Third Hour-at 9:00AM). It seems that the laity participated primarily in Vespers, Matins and Lauds, and in the Midnight Hour (this last was more popular in the East than in the West, but even in the West, Noctures, the prayer during the night, shewed very strong parochial elements). For the modern LotH (for the Latin Church), this shews very marked monastic influence, that was in turn privitized after Trent, even the current LotH is more private than public in nature. In the East, some of the Hours were monastic in origin, but Vespers, Midnight, and Orthros (a composite service of Nocturnes, MAtins, and Lauds) were primarily cathedral (=parochial) in origin, with monastic elements inserted (so Michael’s comment below is not accurate).
Sorry for so many technical terms, but the Divine Office boils down to Psalms, Hymns, and readings, celebrated at certain times of the day (in a perfect world, but strict adherence to time is completely unnecessary-not even all monasteries do this). It is important, however, to remeber that it is not just some monastic thing, but was for many centuries an integral part of a Christian’s life, in particular Vespers, Matins/Lauds, and Divine Liturgy/Mass-with the last being the culmination, or the zenith, but not the sole component, of divine worship.
In Christ,
Adam