The role of the church was to teach Christianity and to aid in saving souls. Over the centuries, as missionaries spread the faith across Europe from Spain to Sweden, they taught the precepts of church doctrine: the immortality of each person’s soul; the Trinity of Father, Son, and Holy Spirit; Jesus’s crucifixion, resurrection, and ascension into heaven; salvation and eternal heavenly life for those judged worthy; and damnation in hell for the rest. One purpose of religious services was to reinforce these lessons for worshippers, making clear the path to salvation through the church’s teachings. This purpose was served chiefly by the liturgy, the texts that were spoken or sung and the rituals that were performed during each service. The role of music was to carry those words, accompany those rituals, and inspire the faithful.

At the same time, the words, prayers, and singing were directed to God, who was in some respects the primary audience.  The daily cycle of services in monasteries and convents, attended only by the participants, reflected the belief that humans on earth, like angels in heaven, should offer unceasing praises to God.  Thus the liturgy and music of the Roman Church had dual aims:  addressing God and reinforcing the faith of those in attendance.

page 43 of _A History of Western Music_.