 The lyrics of many of Armstrong's hymns are believed to have been developed based on rhymed psalters.Some of these psalters include the Book of Psalms for Singing (published by the Board of Education and Publication, Reformed Presbyterian Church of North America), the Psalter Hymnal (published by the Christian Reformed Church), and the Psalms of David in Metre (commonly referred to as the "Scottish Psalter").Armstrong is also thought to have utilized psalm settings by John Milton and William Kethe.