The Directory for Worship of the Orthodox Presbyterian Church says:
"As it is the aim of public worship to glorify God, prayer and praise should predominate in congregational singing. Let every member of the church take part in this act of worship. It should be performed not merely with the lips but with the spirit and the understanding. Since the metrical versions of the Psalms are based upon the Word of God, they ought to be used frequently in public worship. Great care must be taken that all the materials of song are in perfect accord with the teaching of Holy Scripture. Let the tunes as well as the words be dignified and elevated. The stately rhythm of the choral is especially appropriate for public worship. No person shall take a special part in the musical service unless he is a professing Christian and adorns his profession with a godly walk."
Love this! Thanks for sharing this quote from the Directory for Worship of the OPC. I'm a member of the PC(USA), but I think this is relevant to all of us Reformed.