Psalm 150 ends the Psalter, of course, and Augustine’s great work, the Enarrationes in Psalmos. In his commentary he interprets all the reasons the Psalmist gives for praising God as realized in the holy ones in his congregation, and they are all represented in all the instruments the Psalmist calls upon to praise God:

When the Psalmist proposes: “Praise the Lord in his holy ones”: to whom does he say this if not to those same holy ones? And where are they to praise God if not in themselves? For you are his holy ones, you are his power at work in you; and you are his dominion and the multitude of his greatness which he performed and showed in you. You are the trumpet, the psaltery, the harp, the drum, the choir, the strings and organ, and the cymbals of jubilation: all of them making a find sound, because all in harmony. You are all these things. Let nothing cheap, nothing transitory, nothing ludicrous be thought of here.... “Let every spirit praise the Lord!” (EnPs 150, 8; PL 37, 1965-1966)