...work for God should be done with holy joy and cheerfulness.... See what a good Master we serve, who has made it our duty to sing at our work.
On Deut. 28.47-48:
God is a Master that will be served with gladness, and delights to hear us sing at our work.
From the preface to his commentary on the Psalms:
See what a good master we serve, and what pleasantness there is in wisdom's ways, when we are not only commanded to sing at our work, and have cause enough given us to do so, but have words also put in our mouths and songs prepared to our hands.
Matthew Henry, The Pleasure of Being Religious, in The Complete Works of Matthew Henry, Vol. 1, pp. 44, 49:
We may sing at our work, if our minds be by the Spirit of God brought to it, our hands strengthened for it, and our infirmities helped, Rom. viii. 26. and particularly our infirmities in prayer, that by it we may fetch in strength for every service, -- and strength for the day....We should not only be reconciled to our duty, as we ought to be to our greatest afflictions, and make the best of it, but we should rejoice in our duty, and sing at our work.