"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 a combination of sacred music and words, it forms a necessary or integral part of solemn liturgy." 20 The composition and singing of inspired psalms, often accompanied by musical instruments, were already closely linked to the liturgical celebrations of the Old Covenant. the Church continues and develops this tradition: "Address . . . one another in psalms and Hymns and spiritual songs, singing and making melody to the Lord with all your heart." "He who sings prays twice." 21