A metrical psalter is a kind of Bible translation: a book containing a metrical translation of all or part of the Book of Psalms in vernacular poetry, meant to be sung as hymns in a church. Some metrical psalters include melodies or even harmonizations. The composition of metrical psalters was a large enterprise of the Protestant Reformation, especially in its Calvinist manifestation.
During the Protestant Reformation, a number of Bible texts were interpreted as requiring reforms in the music used in worship. The Psalms were particularly commended for singing; James 5:13 asks, "Is anyone happy? Let him sing songs of praise." (James 5:13) Colossians 3:16 states "Let the word of Christ dwell in you richly as you teach and admonish one another with all wisdom, and as you sing psalms, hymns and spiritual songs with gratitude in your hearts to God." (Colossians 3:16)
In the preface to his edition of the Greek New Testament, Erasmus wrote:
The Reformers, taking their cue from these Scriptures and from Erasmus, shared a common interest in Scripture that would be singable.
Various Reformers interpreted these texts as imposing strictures on sacred music. The psalms, especially, were felt to be commended to be sung by these texts. A revival of Gregorian chant, or its adaptation to the vernacular, was apparently not considered. Instead, the need was felt to have metrical vernacular versions of the Psalms and other Scripture texts, suitable to sing to metrical tunes and even popular song forms.