Presbyterian worship after 1650 was built around a rule most other Protestant traditions eventually abandoned: sing only the biblical psalms, set to meter so a congregation could carry them, and sing nothing else. The Scottish Psalter was the concrete form that rule took, and the reasoning behind it was the same conviction John Calvin had built the earlier Genevan Psalter on the previous century, that corporate worship belonged in the church's own inspired words rather than in verse composed by any individual, however gifted or pious. A hymn, on that reasoning, put a human author's theology into the congregation's mouth; a psalm put only scripture there. Exclusive psalmody, as the practice came to be called, held across Scottish Presbyterian worship for roughly two centuries after 1650, sung almost without exception, and it traveled wherever Scottish and Irish Presbyterians settled, carried to America, Canada and Australia by emigrants who brought little else from home that mattered more.
The discipline did not survive everywhere. Mainstream Presbyterian denominations gradually admitted hymns alongside psalms over the eighteenth and nineteenth centuries, but a minority never did. Reformed Presbyterian and Covenanter congregations, descendants of the Scottish Covenanters who had fought and died over the shape of their own worship, still sing the psalter exclusively and without instrumental accompaniment today, treating a three and a half century old translation committee's work as still binding on how they are permitted to address God in song.