The Westminster Directory for Public Worship

Chapter : Of Singing of Psalms.

It is the duty of Christians to praise God publicly, by singing of psalms together in the congregation, and also privately in the family.
In singing of psalms, the voice is to be tunably and gravely ordered; but the chief care must be to sing with understanding, and with grace in the heart, making melody unto the Lord.
That the whole congregation may join herein, every one that can read is to have a psalm book; and all others, not disabled by age or otherwise, are to be exhorted to learn to read. But for the present, where many in the congregation cannot read, it is convenient that the minister, or some other fit person appointed by him and the other ruling officers, do read the psalm, line by line, before the singing thereof.