General Quotes on Psalmody

"The Psalms have been indissoluby bound up with the life, public and private alike, of all Calvinists." -- Émile Doumergue (the most famous biographer of John Calvin)

"This one Ordinance [Psalm-singing] only contributed mightily to the downfall of Popery, and the propagation of the Gospel. It took so much with the genius of the Nation [France], That all ranks and degrees of Men practiced it in the Temples and in their Families. No Gentleman professing the Reformed Religion, would sit down at his Table without praising God by singing. Yea it was a special part of their Morning and Evening Worship, in their several Houses, to sing God's Praises." -- John Quick

"The singing of Psalms has also now just about died out. Originally Reformed churches only allowed congregational singing of the Psalms, because they were authentically and authoritatively Biblical and hence lacked the potential contamination of false teaching which might come from the mere human authorship of hymns. Subsequently, however, hymns (which are not even mentioned by the Confession) have been introduced into Reformed liturgical use and have virtually driven out what is mentioned and was once exclusively sung." -- John H. Gerstner, Douglas F. Kelly, and Philip Rollison, "A Guide to the Westminster Confession of Faith: Commentary," pp. 104-105

Psalms are song by emperors; the common people rejoice in them. Each man does his utmost in singing what will be a blessing to all. Psalms are sung in the home and rehearsed on the streets. The psalm is learned without labor and remembered with delight. Psalmody unites those who disagree, makes friends of those at odds, and brings together those who are out of charity with one another. Who could retain a grievance against the man whom he had joined in singing before God? The singing of praise is the very bond of unity, when the whole people join in a single act of song.

—Ambrose on Psalm 1, Exposition 9, trans. Erik Routley in The Church and Music (London: Duckworth, 1950), 129.

"The Psalms have been indissolubly bound up with the life, public and private alike, of Calvinists." -- Émile Doumergue, "Music in the Work of Calvin," Princeton Theological Review (Vol. VII, No. 4, Oct. 1909, pp. 541-542)

Luther’s “Psalmi Paulini”: 32,51,130,143
“the condemnability of the natural man, the freeness of mercy, and the spiritual nature of redemption are expressed in a manner thoroughly Pauline.” ~ Delitzsch

“I want a name for that man who should pretend that he could make better hymns than the Holy Ghost. His collection is large enough: it wants no addition. It is perfect, as its author, and not capable of any improvement. Why in such a case would any man in the world take it into his head to write hymns for the use of the Church? It is just the same as if he was to write a new Bible, not only better than the old, but so much better, that the old may be thrown aside. What a blasphemous attempt! And yet our hymn-mongers, inadvertently, I hope, have come very near to this blasphemy: for they shut out the Psalms, introduce their own verses into the Church, sing them with great delight, and as fancy with great profit; although the whole practice be in direct opposition to the command of God, and therefore cannot possibly be accompanied by the blessing of God.” ~ William Romaine

~ J.A. Grier, Synoptic Lectures on Theological Subjects (Allegheny Theological Seminary, 1896), p.73Psalm 110 manages in the space of seven verses to encapsulate almost every truth held dear to Christians - the two natures of Christ (vs. 1); the eternal and  unchangeable character of his priesthood (vs. 4); the final judgment of God against the enemies of the Messiah (vs. 5); the eternal rule of Christ from the right hand of God (vss. 1,2); and the rebirth and willing service of the people of God (vs. 3). p.51

“THIS is a true and exalted Psalm, the main one to deal with our dear Lord Jesus Christ. Here, as nowhere else in the Old Testament Scriptures, we find a clear and powerful description of his person - who He is, namely, both David’s promised Son according to the flesh and God’s eternal son, as well as the eternal King and Priest - and of his resurrection, ascenscion, and entire kingdom.” ~ Martin Luther on Psalm 110, Luther’s Works (Concordia, 1957), Vol 13, p.228

“You have here a display of the person and work of the Savior in such fullness and detail as to make us wonder whether those that object to the Psalms on this score have ever read them.” ~ J.A. Grier, Synoptic Lectures on Theological Subjects (Allegheny Theological Seminary, 1896), p.73

 "The Book of Psalms was penned by David, Asaph, Moses and others, and in several ages and states of the church, and were appointed to be sung then, for the present state of the church in those days. It may therefore be demanded: Why then do we sing them now in our churches? The answer is: the church in all ages consists of a number of believers, and the faith is always one, and makes all that apprehend God’s promises to be alike to one another in grace, in meditations, in dispositions, in affections, in desires, in spiritual wants, in the feeling and use of afflictions, in course and conversation of life, and in performance of duties to God and man; and therefore the same psalms, prayers and meditations, are now as fit for the church in these days, and are said and sung with the same use and profit, as in the church in those days when they were first made." -- William Perkins

George Bancroft, The Apostolic Church and the Gospel Ministry, pp. 223-224:

“Some promoters of singing hymns may differ with the [OPC] majority and minority reports, alleging that perhaps the phrase “singing of psalms” in the Westminster Confession of Faith may not mean that only psalms are to be employed in public worship. Some Presbyterians have argued that the term ‘psalms,’ being a lower case ‘p’ might refer to psalms and hymns. In the original 1648 edition of the Westminster Directory for the Publick Worship of God, the upper case ‘P’ in the term ‘Psalms’ was consistently used;16 but regardless of which edition is used with consistent upper or lower case, it will make no difference to the true intent of the writers and signers of the Westminster Standards. The following Westminster documents consistently speak of singing psalms, with no mention of hymns: Westminster Confession of Faith (ch. XXI, sec. V), Westminster Form of Presbyterial Church Government (Of the Ordinances in a particular Congregation), and the Westminster Directory for the Publick Worship of God (Of the Sanctification of the Lord’s Day, Of Singing of Psalms). Acknowledging historic Presbyterian familiarity with the Synod of Dordrecht Church Order (1618-19) and the distinction made between psalms and hymns, in all fairness to legislative intent interpretation, the ‘psalms’ or ‘Psalms’ in the Westminster Standards must be biblical psalms of praise.In the later editions of the Westminster Standards, biblical psalms of praise, were commonly referred to as ‘psalms.’ In the reading of the Scriptures, in the Westminster Directory for the Publick Worship of God, it references exposition of the portion of Scripture read: “let it not be done until the whole chapter of psalm be ended” (Of Public Reading of the Holy Scriptures). Regarding public preaching, it speaks of some ‘text of scripture’; it further orders the use of “some chapter, a psalm, or book of the holy scripture” (Of the Preaching of the Word). In the Directory for the Publick Worship of God, there are parallel and coordinate directives to read or sing a ‘psalm,’ but no directive to sing a hymn. We find this same employment of the term ‘psalm’ or ‘psalms’ in the Authorised King James Version to refer to the Book of Psalms (see Luke 24:44).The London or Baptist Confession of Faith (1689) deliberately altered section V, of the chapter, Of Religious Worship and the Sabbath Day, to read “psalms, hymns, and spiritual songs.” The Baptists understood the legislative intent meaning of the Westminster Confession of Faith to be psalms only, as Ephesians 5:19 and Colossians 3:16 are used as proof-texts for the “singing of psalms with grace in the heart” (West. Con. ch. XXI, sec. V). The Baptists, therefore, decidedly rejected the historic Westminster Presbyterian interpretation of Ephesians 5:19 and Colossians 3:16. The 17th century Westminster Presbyterians interpreted, “psalms, hymns, and spiritual songs” (Eph. 5:19; Col. 3:16) to the Book of Psalms. 16 The Westminster Standards, An Original Facsimile (Audubon, New Jersey: Old Paths Publications, 1997).”

Folks that hold to exclusivity of Psalm singing derive the idea from sola scriptura and God’s regulative principle;  They sing the Psalms because they find a prescription for it in scripture; they don’t sing songs outside of the 150 psalms because they do not see such a clear warrant to do so. No warrant, we avoid it.

1Chr. 16:9 Sing to Him, sing psalms to Him;Talk of all His wondrous works!
Psa. 95:1   Oh come, let us sing to the LORD!Let us shout joyfully to the Rock of our salvation.2 Let us come before His presence with thanksgiving;Let us shout joyfully to Him with psalms.
Psa. 98:5 Sing to the LORD with the harp,With the harp and the sound of a psalm
Psa. 105:2 Sing to Him, sing psalms to Him;Talk of all His wondrous works!
Eph. 5:19 speaking to one another in psalms and hymns and spiritual songs, singing and making melody in your heart to the Lord,
Col. 3:16 Let the word of Christ dwell in you richly in all wisdom, teaching and admonishing one another in psalms and hymns and spiritual songs, singing with grace in your hearts to the Lord.James
5:13   Is anyone among you suffering? Let him pray. Is anyone cheerful? Let him sing psalms.

Notice how we can see the clear command to sing the Psalms. Nowhere in the canon do we find the command to sing anything otherwise. I know what you are thinking, ‘Scott, Eph 5 and Col 3 says, ‘hymns and spiritual songs’. I address this item later on in this paper.
Source: http://www.semperreformanda.com/the-regulative-principle-of-worship/the-regulative-principle-of-worship-articlesindex/the-regulative-principle-worship-psalm-singing-and-grape-juice/

"So reverentially did the Scottish churches regard Calvin's interpretation of Scripture that authorizations for organs in the various branches of the Presbyterian Church were delayed until 1866 for the Established Church, 1872 for the United Presbyterian Church, and 1883 for the Free Church. And, of course, the ultra-Calvinist Reformed Presbyterian Church of North America even now forbids the use of organs and the singing of hymns." -- Robert Stevenson, "Patterns of Protestant Church Music" (1953), p. 18

 Thomas Clark (1720-1792): “So after nigh seven years labour and critical care, spent on it by both Assemblies and Parliaments, it may be called the Assemblies Metre Version of the Book of Psalms; and they have brought it so very close to represent the same ideas of things, the same doctrines, precepts, &c. as the Hebrew Psalms, wrote also in Hebrew Metre, that those who use it may with great propriety be said to praise the Lord with the words of David and Asaph &c. according to the commandment forecited, 2 Chron. xxix. 30.” —Plain Reasons, Why neither Dr. Watt’s Imitations of the Psalms, nor his other Poems, nor any other human Composition, ought to be used in the Praises of the Great God our Saviour—but, that a Metre Version of the Book of Psalms, examined, with wise and critical Care, by pious and learned Divines, and found by them to be as near the Hebrew Metre Psalms, as the Idiom of the English Language would admit, ought to be used (Albany: Balentine & Webster, 1783), p. 16