Pope Saint Clement, who ruled from 92 to 101 A.D., was the first pope to make a decree concerning Sacred Music. The distinction he made was that liturgical chant (psalms and hymns) should be sung during the liturgy but must not be sung outside of the liturgy. This distinction both promoted the use of liturgical chants and hymns and also protected this same chant from profane use.
“In the pagan festivals, let us not sing the psalms, and let us not read the Scriptures, for fear of seeming like the wandering minstrels, singers and tellers of tales of high adventure, who perform their art for a mouthful of bread. It is not fitting that thus we sing the canticles of the Lord in a strange land.”
– Pope St. Clement in his Epistle to the Corinthians
from Papal Legislation on Sacred Music by Robert F. Hayburn