Kind of self-explanatory: this is a collection of all the Psalms, done almost entirely in common meter for communal singing. The simplicity of the renderings is often really beautiful, and the descriptions, prayers, introductions (including "A Short Treatise on Musicke") are historically fascinating. You can tell that the printers were loving their new capabilities, with little illustrated pointing fingers and the like introducing various phrases and the like: my absolute favorite, above an inset graphic of the musical scale, says "Reader, observe this table." Worth your time, will possibly make you holier, will certainly make you more familiar with the mid-sixteenth century.