21 The church has not been really founded, and is not yet fully alive, nor is it a perfect sign of Christ among men, unless there is a laity worthy of the name working along with the hierarchy. For the Gospel cannot be deeply grounded in the abilities, life and work of any people without the active presence of laymen. Therefore, even at the very founding of a Church, great attention is to be paid to establishing a mature, Christian laity. For the lay faithful fully belong at one and the same time both to the People of God and to civil society: they belong to the nation in which they were born; they have begun to share in its cultural treasures by means of their education; they are joined to its life by manifold social ties; they are cooperating in its progress by their efforts, each in his own profession; they feel its problems to be their very own, and they are trying to solve them. They also belong to Christ, because they were regenerated in the Church by faith and by baptism, so that they are Christ's in newness of life and work (cf. 1 Cor. 15:23), in order that in Christ, all things may be made subject to God, and finally God will be all in all (cf. Cor. 15:28). Their main duty, whether they are men or women, is the witness which they are bound to bear to Christ by their life and works in the home, in their social milieu, and in their own professional circle. In them, there must appear the new man created according to God in justice and true holiness (cf. Eph. 4:24). But they must give expression to this newness of life in the social and cultural framework of their own homeland, according to their own national traditions. They must be acquainted with this culture; they must heal it and preserve it; they must develop it in accordance with modern conditions, and finally perfect it in Christ, so that the Faith of Christ and the life of the Church are no longer foreign to the society in which they live, but begin to permeate and to transform it. Let them be one with their fellow countrymen in sincere charity, so that there appears in their way of life a new bond of unity and of universal solidarity, which is drawn from the mystery of Christ. Let them also spread the Faith of Christ among those with whom they live or have professional connections - an obligation which is all the more urgent, because very many men can hear of Christ and of the Gospel only by means of the laity who are their neighbors. In fact, wherever possible, the laity should be prepared, in more immediate cooperation with the hierarchy, to fulfill a special mission of proclaiming the Gospel and communicating Christian teachings, so that they may add vigor to the nascent Church. Let the clergy highly esteem the arduous apostolate of the laity. Let them train the laity to become conscious of the responsibility which they as members of Christ have for all men; let them instruct them deeply in the mystery of Christ, introduce them to practical methods, and be at their side in difficulties, according to the tenor of the Constitution Lumen Gentium and the Decree Apostolicam Actuositatem. While pastors and laymen, then, retain each their own state of life and their own responsibilities, let the whole young church render one firm and vital witness to Christ, and become a shining beacon of the salvation which comes to us in Christ.
Source: Ad Gentes (Vatican.va)