The musical tradition of the universal Church is a treasure of inestimable value, greater even than that of any other art. The main reason for this pre-eminence is that, as sacred song united to the words, it forms a necessary or integral part of the solemn liturgy.
Holy Scripture, indeed, has bestowed praise upon sacred song, and the same may be said of the fathers of the Church and of the Roman pontiffs who in recent times, led by St. Pius X, have explained more precisely the ministerial function supplied by sacred music in the service of the Lord.
Therefore, sacred music is to be considered the more holy in proportion as it is more closely connected with the liturgical action, whether it adds delight to prayer, fosters unity of minds, or confers greater solemnity upon the sacred rites. But the Church approves of all forms of true art having the needed qualities, and admits them into divine worship.
-Constitution on the Sacred Liturgy, Sacrosanctum Concilium # 112