Always and everywhere, even among pagan peoples, sacred song and the art of music have been used to ornament and decorate religious ceremonies. This is proved by many documents, both ancient and new. These arts have been used especially for the worship of the true and sovereign God from the earliest times. The tunes of these hymns, which are often sung in the language of the people, are memorized with almost no effort or labor. The mind grasps the words and the music. They are frequently repeated and completely understood. Hence even boys and girls, learning these sacred hymns at a tender age, are greatly helped by them to know, appreciate and memorize the truths of the faith. Therefore they also serve as a sort of catechism.
There are many statements of the fathers and ecclesiastical writers testifying that after freedom and peace had been restored to the Church the psalms and hymns of liturgical worship were in almost daily use. Moreover, new forms of sacred chant were gradually created and new types of songs were invented. These were developed more and more by the choir schools attached to cathedrals and other important churches, especially by the School of Singers in Rome. The Sovereign Pontiffs have always diligently fulfilled their obligation to be vigilant in this matter. The Council of Trent also forbids "those musical works in which something lascivious or impure is mixed with organ music or singing." In addition, not to mention numerous other Sovereign Pontiffs, Benedict XIV in an encyclical letter dated 19 February 1749 particularly urged Bishops to firmly forbid the illicit and immoderate elements which had arrogantly been inserted into sacred music. Leo XII, Pius VII, Gregory XVI, Pius IX, and Leo XIII followed the same line.
It is the intention of the Church, however, to protect sacred music against anything that might lessen its dignity, since it is called upon to take part in something as important as divine worship. On this score sacred music obeys laws and rules which are no different from those prescribed for all religious art and, indeed, for art in general. These laws and standards for religious art apply in a stricter and holier way to sacred music because sacred music enters more intimately into divine worship than many other liberal arts, such as architecture, painting and sculpture. These last serve to prepare a worthy setting for the sacred ceremonies. Sacred music, however, has an important place in the actual performance of the sacred ceremonies and rites themselves. Hence the Church must take the greatest care to prevent whatever might be unbecoming to sacred worship or anything that might distract the faithful in attendance from lifting their minds up to God from entering into sacred music, which is the servant, as it were, of the sacred liturgy. Some artists, gravely offending against Christian piety, have dared to bring into churches works devoid of any religious inspiration and completely at variance with the right rules of art. They try to justify this deplorable conduct by plausible-looking arguments which they claim are based on the nature and character of art itself. They go on to say that artistic inspiration is free and that it is wrong to impose upon it laws and standards extraneous to art, whether they are religious or moral, since such rules seriously hurt the dignity of art and place bonds and shackles on the activity of an inspired artist.
These laws warn that great prudence and care should be used in this serious matter in order to keep out of churches polyphonic music which, because of its heavy and bombastic style, might obscure the sacred words of the liturgy by a kind of exaggeration, interfere with the conduct of the liturgical service or, finally, lower the skill and competence of the singers to the disadvantage of sacred worship. (Papal Encyclical, Musicae Sacrae, 25 December 1955).