9 The monastic life, that venerable institution which in the course of a long history has won for itself notable renown in the Church and in human society, should be preserved with care and its authentic spirit permitted to shine forth ever more splendidly both in the East and the West. The principal duty of monks is to offer a service to the divine majesty at once humble and noble within the walls of the monastery, whether they dedicate themselves entirely to divine worship in the contemplative life or have legitimately undertaken some apostolate or work of Christian charity. Retaining, therefore, the characteristics of the way of life proper to them, they should revive their ancient traditions of service and so adapt them to the needs of today that monasteries will become institutions dedicated to the edification of the Christian people. Some religious communities according to their rule or constitutions closely join the apostolic life to choir duty and monastic observances. These should so adapt their manner of life to the demands of the apostolate appropriate to them that they observe faithfully their way of life, since it has been of great service to the Church.
Source: Perfectae Caritatis (Vatican.va)