The Ancient and Modern Mode of Singing the Psalms historically demonstrates how the Old Testament saints, the early New Testament Christians and almost all Presbyterians (after adopting the Westminster Standards) sang the Psalms by "lining them out" (e.g. see the Westminster Directory for Public Worship).

Musical instruments, a Papal innovation, were also unheard of among faithful Reformers and "denominated the ensigns of Baal." Basically a blast against "all the refined idolatries of the churches" of the author's time.

It also lays out the numerous advantages of lining out the Psalms -- especially for including younger (pre-reading age) children in the praises of God.