This kind [the motet] of all others which are made on a ditty [text], requireth most art, and moveth and causeth most strange effects in the hearer, being aptly framed for the ditty and well expressed by the singer, for it will draw the auditor (and especially the skilful auditor) into a devout and reverent kind of consideration of him fro whose praise it was made. But I see not what passions or motions it can stir up, being sung as most men do commonly sing it: that is, leaving out the ditty and singing only the bare note, as it were a music made only for instruments, which will indeed show the nature of the music, but never. Carry the spirit and (as it were) that lively soul which the ditty giveth, but of this enough.
And to return to the expressing of the ditty, the matter is now come to that state that though a song be never so well made and never so aptly applied to the words, yet shall you hardly find singers to express it as it ought to be, for most of our church men, (so they can cry louder in the choir than their fellows) care for no more, whereas by the contrary, they ought to study how to vowel and sing clean, expressing their words with devotion and passion, whereby to draw the hearer as it were in chains of gold by the ears to the consideration of holy things.
But this for the most part, you shall find amongst them, that let them continue never so long in the church, yea though it were twenty years, they will never study to sing better than they did the first day of their preferment to that place, so that it should seem that having obtained the living which they sought for, they have little or no care at all either of their own credit, or well discharging of that duty whereby they have their maintenance.
Thomas Morley, A Plain and Easy Introduction to Practical Music (London: Peter Short, 1597). Spellings modernised for ease of reading.
The painting below is by Egbert van Heemskerk, and depicts a group of mid seventeenth-century monks singing, seemingly rather raucously. Note, however, that the tactus is still being indicated by one of the singers.