71 Missionaries should likewise be mindful of the fact that, from the beginning, when the Catholic Church sent preachers of the Gospel into lands not yet illumined by the light of faith, it took care to bring into those countries, along with the sacred liturgical rites, musical compositions, among which were the Gregorian melodies. It did this so that the people who were to be converted might be more easily led to accept the truths of the Christian religion by the attractiveness of these melodies.
Source: Musicae Sacrae (Vatican.va)