18 It is now time, Venerable Brothers and Beloved Sons, that We speak to you who, because of your long labors and wise service as missionaries among the heathen, have been found worthy to be promoted by Apostolic authority to the office of Vicars and Prefects. First of all, We speak of the general progress which the missions have made in the last few years due to your charity and zeal, for which progress We offer congratulations both to you and to the missionaries under your charge. What your principal duties are and what you especially have to guard against in the discharge of these duties, has already been set forth with such wisdom and eloquence by Our immediate Predecessor that nothing along that line needs be added to his words. However, over and above that, We deem it well, Venerable Brothers and Beloved Sons, to make known Our own mind on certain matters.
Source: Rerum Ecclesiae (Vatican.va)