10 As sharers in the role of Christ as priest, prophet, and king, the laity have their work cut out for them in the life and activity of the Church. Their activity is so necessary within the Church communities that without it the apostolate of the pastors is often unable to achieve its full effectiveness. In the manner of the men and women who helped Paul in spreading the Gospel (cf. Acts 18:18, 26; Rom. 16:3) the laity with the right apostolic attitude supply what is lacking to their brethren and refresh the spirit of pastors and of the rest of the faithful (cf. 1 Cor. 16:17-18). Strengthened by active participation in the liturgical life of their community, they are eager to do their share of the apostolic works of that community. They bring to the Church people who perhaps are far removed from it, earnestly cooperate in presenting the word of God especially by means of catechetical instruction, and offer their special skills to make the care of souls and the administration of the temporalities of the Church more efficient and effective. The parish offers an obvious example of the apostolate on the community level inasmuch as it brings together the many human differences within its boundaries and merges them into the universality of the Church. The laity should accustom themselves to working in the parish in union with their priests, bringing to the Church community their own and the world's problems as well as questions concerning human salvation, all of which they should examine and resolve by deliberating in common. As far as possible the laity ought to provide helpful collaboration for every apostolic and missionary undertaking sponsored by their local parish. They should develop an ever-increasing appreciation of their own diocese, of which the parish is a kind of cell, ever ready at their pastor's invitation to participate in diocesan projects. Indeed, to fulfill the needs of cities and rural areas, they should not limit their cooperation to the parochial or diocesan boundaries but strive to extend it to interparochial, interdiocesan, national, and international fields. This is constantly becoming all the more necessary because the daily increase in mobility of populations, reciprocal relationships, and means of communication no longer allow any sector of society to remain closed in upon itself. Thus they should be concerned about the needs of the people of God dispersed throughout the world. They should especially make missionary activity their own by giving material or even personal assistance. It is a duty and honor for Christians to return to God a part of the good things that they receive from Him.
Source: Apostolicam Actuositatem (Vatican.va)