63 If hymns of this sort are to bring spiritual fruit and advantage to the Christian people, they must be in full conformity with the doctrine of the Catholic faith. They must also express and explain that doctrine accurately. Likewise they must use plain language and simple melody and must be free from violent and vain excess of words. Despite the fact that they are short and easy, they should manifest a religious dignity and seriousness. When they are fashioned in this way these sacred canticles, born as they are from the most profound depths of the people's soul, deeply move the emotions and spirit and stir up pious sentiments. When they are sung at religious rites by a great crowd of people singing as with one voice, they are powerful in raising the minds of the faithful to higher things.
Source: Musicae Sacrae (Vatican.va)