20 Since the particular church is bound to represent the universal Church as perfectly as possible, let it realize that it has been sent to those also who are living in the same territory with it, and who do not yet believe in Christ. By the life witness of each one of the faithful and of the whole community, let the particular church be a sign which points out Christ to others. Furthermore, there is need of the ministry of the word, so that the Gospel may reach all. The bishop should be first and foremost a herald of the Faith, who leads new disciples to Christ. In order that he may properly fulfill this noble task, let him thoroughly study both the conditions of his flock, and the private opinions of his countrymen concerning God, taking careful note also of those changes which urbanization, migrations, and religious indifferentism have introduced. The local priests in the young churches should zealously address themselves to the work of spreading the Gospel, and join forces with the foreign missionaries who form with them one college of priests, united under the authority of the bishop. They should do this, not only with a view to the feeding the faithful flock, and to the celebrating of divine worship, but also to the preaching of the Gospel to those outside, let them show themselves ready, and when the occasion presents itself, let them with a willing heart offer the bishop their services for missionary work in distant and forsaken areas of their own diocese or of other dioceses. Let religious men and women, and the laity too, show the same fervent zeal toward their countrymen, especially toward the poor. Episcopal conferences should see to it that biblical, theological, spiritual and pastoral refresher courses are held at stated intervals with this intention, that amid all vicissitudes and changes the clergy may acquire a fuller knowledge of the theological sciences and of pastoral methods. For the rest, those things which this council has laid down, particularly in the Decree on the Life and Work of Priests, should be religiously observed. In order that this missionary work of the particular church may be performed, there is need of qualified ministers, who are to be prepared in due time in a way suited to the conditions of each church. Now since men are more and more banding together into associations, it is very fitting that episcopal conferences should form a common plan concerning the dialogue to be held with such associations. But if perchance in certain regions, groups of men are to be found who are kept away from embracing the Catholic Faith because they cannot adapt themselves to the peculiar form which the church has taken in there, it is hoped that this condition will be provided for in a special way, until such time as all Christians can gather together in one community. Let..individual bishops call to their dioceses the missionaries whom the Holy See may have on hand for this purpose; or let them receive such missionaries glad]y, and support their undertakings effectively. In order that this missionary zeal may flourish among those in their own homeland, it is very fitting that the young churches should participate as soon as possible in the universal missionary work of the Church, and send their own missionaries to proclaim the Gospel all over the world, even though they themselves are suffering from a shortage of clergy. For their communion with the universal Church will be somehow brought to perfection when they themselves take an active part in missionary zeal toward other nations.
Source: Ad Gentes (Vatican.va)