As usual Locke wrote an aggressive Preface to Psyche. It begins:
That Poetry and Musick, the chief manifestives of Harmonical Phancy, should provoke such discordant effects in many is more to be pityed than wondered at: it having become a fashionable art to peck and carp at other men's conceptions, how mean soever their own are. Expecting, therefore, to fall under the lash of some soft-headed or hard-hearted composers (for there are too many better at finding of faults than mending them) I shall endeavour to remove these few blocks which perhaps they may take occasion to stumble at.
He goes on to say the title Opera is of the Italian, and claims that as far as his ability could reach, he had written agreeably to the design of the author, and that the variety of his setting was never in Court or Theatre till now presented to the nation, "though I must confess there has been something done, and more by me than any other of this kind."
Locke evidently considered Psyche as a real Opera and a novelty in this country. The work was dedicated to James, Duke of Monmouth, who (the composer says) "gave this life by your often hearing this practised and encouraged and heartened the almost heartless undertakers and performers."
Amongst his other works was one called Melothesia, or Certain general Rules for playing upon a continued Bass. This is said to be the first book of its kind, and he contributed to many other works. Roger North tells us "Locke set most of the Psalms to music in parts for the use of some vertuoso ladyes in the City, and he composed a magnifick Consort of four parts after the old style which is the last that hath been made."
His life was not long, but it was important, and perhaps the greatest tribute to his memory was that Henry Purcell wrote an ode commemorative of his decease "On the death of his worthy friend Mr Matthew Locke, Music Composer in Ordinary to His Majesty, and Organist of Her Majesty's Chappell, who dyed in August, 1677."