Of Prayer, by John Calvin, tr. Henry Beveridge , at sacred-texts.com
Hence it is perfectly clear that neither words nor singing (if used in prayer) are of the least consequence, or avail one iota with God, unless they proceed from deep feeling in the heart. Nay, rather they provoke his anger against us, if they come from the lips and throat only, since this is to abuse his sacred name, and hold his majesty in derision. This we infer from the words of Isaiah, which, though their meaning is of wider extent, go to rebuke this vice also: "Forasmuch as this people draw near me with their mouth, and with their lips do honour me, but have removed their heart far from me, and their fear toward me is taught by the precept of men: therefore, behold, I will proceed to do a marvellous work among this people, even a marvellous work and a wonder: for the wisdom of their wise men shall perish, and the understanding of their prudent men shall be hid" (Isaiah 29:13). Still we do not condemn words or singing, but rather greatly commend them, provided the feeling of the mind goes along with them. For in this way the thought of God is kept alive on our minds, which, from their fickle and versatile nature, soon relax, and are distracted by various objects, unless various means are used to support them. Besides, since the glory of God ought in a manner to be displayed in each part of our body, the special service to which the tongue should be devoted is that of singing and speaking, inasmuch as it has been expressly created to declare and proclaim the praise of God. This employment of the tongue is chiefly in the public services which are performed in the meeting of the saints. In this way the God whom we serve in one spirit and one faith, we glorify together as it were with one voice and one mouth; and that openly, so that each may in turn receive the confession of his brother's faith, and be invited and incited to imitate it.