21 Perhaps it may be said that sufficient\attention has never been paid to the method whereby the Gospel began to be preached and the Church of God established all over the world. We touched on this subject briefly at the closing of the Missionary Exhibition and recalled the fact that from a study of the earliest monuments of Christian antiquity it is clearly evident that the clergy placed in charge of the faithful in each new community by the Apostles were not men brought in from the outside but were chosen from the natives of that locality. From the fact that the Roman Pontiff has entrusted to you and to your assistants the task of preaching the Christian religion to pagan nations, you ought not to conclude that the role of the native clergy is merely one of assisting the missionaries in minor matters, of merely following up and completing their work. What, We ask, is the true object of these holy missions if it be not this, that the Church of Christ be founded and established in these boundless regions? How can the Church among the heathens be developed today unless it be built of those very elements out of which our own churches were built; that is to say, unless it be made up of people, clergy, and religious orders of men and women recruited from the native populations of the several regions? Why should the native clergy be forbidden to cultivate their own portion of the Lord's vineyard, be forbidden to govern their own people? In order to enable you to progress in winning from heathenism new converts to Christ, would it not be of great assistance if you would entrust to the native clergy the people already converted so that they could minister to them and preserve their faith? As a matter of fact, the native clergy will prove to be most useful (more useful than some people imagine in extending the Kingdom of Christ "for since the native priest," to quote Our Predecessor, "by birth, temper, sentiment, and interests is in close touch with his own people, it is beyond all controversy how valuable he can be in instilling the Faith into the minds of his people. The native priest understands better than any outsider how to proceed with his own people. Such being the case, he can often gain access to places where a foreign priest would not be permitted to enter." (Apostolic letter Maximum Illud )
Source: Rerum Ecclesiae (Vatican.va)