21 Therefore, making use of their judgment and cooperation, bishops will take care to establish, at opportune moments, study centers to meet the needs of one or more regions in order to make basic doctrine known and understood. In these, both foreign and local priests can employ their learning and experience to benefit the particular countries in which they were born or in which they have chosen to spread the Christian truth. In this connection, We should also like to quote the teaching of Our immediate predecessor Pius XII, expressed in these words: there must be promoted "the publication and dissemination of Catholic books of every description"; (39) and care must be taken to advance "the use of modern means of communication in spreading Christian doctrine. No one can ignore the importance of gaining the good will of native peoples and making them favorable to Catholicism." (40) Certainly, all methods cannot be employed in all places; all opportunities must be taken, however, to fulfill different needs, whenever they arise, even though, sometimes, "one sows, another reaps." (41)
Source: Princeps Pastorum (Vatican.va)