46 She has repeatedly shown in her missionary enterprises that such a principle of action is the guiding star of her universal apostolate. Pioneer research and investigation, involving sacrifice, devotedness and love on the part of her missionaries of every age, have been undertaken in order to facilitate the deeper appreciative insight into the most varied civilizations and to put their spiritual values to account for a living and vital preaching of the Gospel of Christ. All that in such usages and customs is not inseparably bound up with religious errors will always be subject to kindly consideration and, when it is found possible, will be sponsored and developed.
Source: Summi Pontificatus (Vatican.va)