TLS reaffirmed the primacy of Gregorian chant, which had largely fallen out of favor, and the superiority of Renaissance polyphony, especially that of Giovanni Pierluigi da Palestrina, over other, later polyphonic music. It recognized that some modern compositions are "of such excellence, sobriety and gravity, that they are in no way unworthy of the liturgical functions", but warned that they needed to be "free from reminiscences of motifs adopted in the theaters, and be not fashioned even in their external forms after the manner of profane pieces".
The text reaffirms Gregorian chant's importance and praises Renaissance polyphony, particularly Palestrina's work. It acknowledges some modern compositions as worthy for liturgical use but warns against borrowing theatrical motifs or imitating secular styles.