Some historical data on Psalm singing:
“Council of Laodicea (343-381), canon LIX: “No psalms composed by private individuals nor any uncanonical books may be read in the church, but only the Canonical Books of the Old and New Testaments.”
Council of Braga (563): “no poetic composition be sung in the Church except the Psalms of the sacred canon..”
National Synod of Dort, 1578, Art. 76.: “The Psalms of David, in the edition of Petrus Dathenus, shall be sung in the Christian meetings of the Netherlands Churches (as has been done until now), abandoning the hymns which are not found in Holy Scripture.”
National Synod of Middelburg, 1581, Art. 51.: “Only the Psalms of David shall be sung in the church, omitting the hymns which one cannot find in Holy Scripture.”
National Synod of Gravenhage, 1586, Art. 62.:“The Psalms of David shall be sung in the churches, omitting the hymns which one does not find in Holy Scripture.”
Westminster Confession of Faith 21:5 (1646): “The reading of the Scriptures with godly fear; the sound preaching, and conscionable hearing of the word, in obedience unto God, with understanding, faith, and reverence; singing of psalms with grace in the heart [Col.3:16; Eph.5:19; James 5:13]; as also the due administration and worthy receiving of the sacraments instituted by Christ; are all parts of the ordinary religious worship of God: besides religious oaths and vows, solemn fastings, and thanksgivings upon special occasions, which are, in their several times and seasons, to be used in a holy and religious manner.”