1 Chronicles 25

We read in the first book of Paralipomena that when the prophet David grew old in years devoted to the Lord, he chose four thousand young men from the people of Israel to render the psalms, which he had composed through the Lord's inspiration, so as to attain the great sweetness of heavenly grace by means of pipes, lyres, harps, timbrels, cymbals, trumpets, and their own voices. This sweet harmony clearly comprised a threefold division: a rational part consisting of the human voice, an irrational part comprising musical instruments and a common part resulting from the fusion of the two, such that the human voice issued forth in fixed melody and the tune of the instruments joined in harmonious accompaniment. With this performance the sweet and pleasant music presaged the Catholic church, which by the Lord's gift was to believe with varied tongues and diverse blending in the single harmony of faith.