Of Prayer, by John Calvin, tr. Henry Beveridge [1845], at sacred-texts.com
It is also plain that the public prayers are not to be couched in Greek among the Latins, nor in Latin among the French or English (as hitherto has been every where practised), but in the vulgar tongue, so that all present may understand them, since they ought to be used for the edification of the whole Church, which cannot be in the least degree benefited by a sound not understood. Those who are not moved by any reason of humanity or charity, ought at least to be somewhat moved by the authority of Paul, whose words are by no means ambiguous: "When thou shalt bless with the spirit, how shall he that occupieth the room of the unlearned say, Amen, at thy giving of thanks, seeing he understandeth not what thou sayest? For thou verily givest thanks, but the other is not edified" (1 Cor. 14:16, 17). How then can one sufficiently admire the unbridled license of the Papists, who, while the Apostle publicly protests against it, hesitate not to bawl out the most verbose prayers in a foreign tongue, prayers of which they themselves sometimes do not understand one syllable, and which they have no wish that others should understand? 21 Different is the course which Paul prescribes, "What is it then? I will pray with the spirit, and I will pray with the understanding also; I will sing with the spirit, and I will sing with the understanding also:" meaning by the spirit the special gift of tongues, which some who had received it abused when they dissevered it from the mind, that is, the understanding. The principle we must always hold is, that in all prayer, public and private, the tongue without the mind must be displeasing to God. Moreover, the mind must be so incited, as in ardour of thought far to surpass what the tongue is able to express. Lastly, the tongue is not even necessary to private prayer, unless in so far as the internal feeling is insufficient for incitement, or the vehemence of the incitement carries the utterance of the tongue along with it. For although the best prayers are sometimes without utterance, yet when the feeling of the mind is overpowering, the tongue spontaneously breaks forth into utterance, and our other members into gesture. Hence that dubious muttering of Hannah (1 Samuel 1:13), something similar to which is experienced by all the saints when concise and abrupt expressions escape from them. The bodily gestures usually observed in prayer, such as kneeling and uncovering of the head (Calv. in Acts 20:36), are exercises by which we attempt to rise to higher veneration of God.
21 French, "Qui est-ce donc qui se pourra assez esmerveiller d’une audace tant effrenee qu’ont eu les Papistes et ont encore, qui contre la defense de l’Apostre, chantent et brayent de langue estrange et inconnue, en laquelle le plus souvent ils n'entendent pas eux mesmes une syllabe, et ne veulent que les autres y entendent?"—Who then can sufficiently admire the unbridled audacity which the Papists have had, and still have, who, contrary to the prohibition of the Apostle, chant and bray in a foreign and unknown tongue, in which, for the most part, they do not understand one syllable, and which they have no wish that others understand?