86 Priests who are engaged in the sacred pastoral ministry will offer the praises of the hours with greater fervor the more vividly they realize that they must heed St. Paul's exhortation: "Pray without ceasing" (1 Thess. 5:11). For the work in which they labor will effect nothing and bring forth no fruit except by the power of the Lord who said: "Without me you can do nothing" (John 15: 5). That is why the apostles, instituting deacons, said: "We will devote ourselves to prayer and to the ministry of the word" (Acts 6:4). 81. In order that the divine office may be better and more perfectly prayed in existing circumstances, whether by priests or by other members of the Church, the sacred Council, carrying further the restoration already so happily begun by the Apostolic See, has seen fit to decree as follows concerning the office of the Roman rite.
Source: Sacrosanctum Concilium (Vatican.va)