I will say at the outset that I have already addressed this subject on the Puritanboard
here.
A line of questioning to my brothers who hold to exclusive psalmody. How much flexibility is allowed in the pursuit of singing psalms in worship?
1. May we transform the psalm by setting it to rhyme and meter?
No, not transform. Yes we may render it faithfully if we adapt the Hebrew to an English translation and retain the original words and meanings without superfluous additions and significant detractions.
2. May we transform the psalm by only singing part of the psalm? Many of Calvin's psalms in the beautiful Genevan Psalter are only parts of psalms because the psalms are very long.
No, not transform. Yes to singing a portion as the New Testament at times quotes portions of Psalms without changing the meaning of the whole (as well as approved examples: Luke 19:38). The command to sing the Psalms is general and preceptive; the particulars are left to the light of nature and common sense.
3. May we transform the psalm by making explicit Christological connections that are in the psalms so that we explicitly sing about Jesus in worship?
No, not transform. Yes to "singing with grace in your hearts to the Lord." The explicitly Christological nature is revealed in the original words and in their application or use in the New Testament. The Psalms as written are sufficiently Christological for Paul to use them copiously throughout Hebrews to prove the greater light and glory of the new covenant:
https://kingandkirk.com/kings-songs...salmodically-mediated-in-the-book-of-hebrews/
Changing the Psalms not only commits one to mishandling and misrepresenting God's Word, but erects a man made wall between parties in the commonwealth of Israel. The so called ambiguity of the Psalms lent itself to the language of its redemptive period: for Israel as a child and now Christians can sing the same words with the new meaning of God's revelation in Christ. Thus the church is one in all ages.
If we may transform psalms by setting them to rhyme and meter, only singing parts of psalms, and making Christological connections explicit, then what is the relevant difference between such a transformed psalm and one of Isaac Watts' or Charles Wesley's hymns?
Isaac Watts did change the Psalms substantially. J.G. Vos highlights the differences between Watts' songs and those of the Psalms, particularly in light of the history of the Bible:
"Evil is not abstract, but concrete; it is identified with particular persons. To destroy the evil, the persons must be dealt with by God’s mighty power and righteous judgment. Isaac Watts said he would make David talk like a Christian. He denatured the Psalms, and he sophisticated them. Watts quite failed to appreciate the real beauty and glory of the Psalter. Since Watts time, some Psalm-singing denominations have shied away from the proper names in the Psalter, and have tried to screen many of them out of it. Zion is changed to “the church,” and Jerusalem likewise; many of the others are omitted or smoothed over in some way. This yields us a denatured Psalter. No wonder the next step is to give up the Psalms in worship. They have already given up the real vigor and beauty and power of the Psalms by omitting the proper names."
https://bluebanner.org/assets/pdfs/tenst.pdf
You don't really believe that Wesley's hymns are in any way comparable to the inspired word of God, do you? You cannot seriously believe that "And Can It Be?" compares, in any way, to any particular Psalm.
Assuming that you believe that God has commanded the singing of the Psalms, then the contradiction between singing a rhymed and metered version of the Psalms and singing the Psalms as you think a consistent adherent of exclusive psalmody
should is your problem as well.
Assuming, also, your sincerity in asking, and not some clever ploy on your part to trap us in a logical fallacy, then why don't you suggest a better way to render the Psalms that we can sing them as you think they should be rendered?
Finally, assuming your point is proven, all it proves is that we are inconsistent. It does not prove that one should sing uninspired songs in worship nor does it prove that the Psalms are insufficient for worship.