59 We ourselves made the following statement in the first Encyclical Letter We wrote, Summi Pontificatus : "Persevering research carried out with laborious study, on the part of her missionaries of every age, has been undertaken in order to facilitate the deeper appreciative insight into the various civilizations and to utilize their good qualities to facilitate and render more fruitful the preaching of the Gospel of Christ. Whatever there is in the native customs that is not inseparably bound up with superstition and error will always receive kindly consideration and, when possible, will be preserved intact."
Source: Evangelii Praecones (Vatican.va)