I am finally getting around to posting the Scriptural argument against Exclusive Psalmody.
Let us just start with Scriptural commands to sing things other than psalms. Remember there is a specific word for psalm. There is debate about whether psalm (the word) means The Psalms always, but we can set that aside for now. Even if we concede it, I think the evidence is on the hymn singing side. Ephesians 5:19 and Colossians 3:16 are the most famous. Here Christians are commanded to sing psalms, hymns, and spiritual songs. Granting that psalms here means The Psalms, there seems little possible evidence that hymns and spiritual songs also mean psalms. And as you would expect few Greek scholars even claim they mean the same thing. Not even John Calvin claims that this is in favor of exclusive psalmody. Some want to claim that the use of “kai” (translated and) connects the three making them into three ways of saying one thing. But that argument breaks down as “kai” is not used in Colossians 3:16.
Then of course there is also the command to “sing a new song” (Isaiah 42:10). The word there is “hymn” and not the word “psalm”. The word for psalm exists, but was not used. Thus, here we have a command to sing hymns. The only way to maintain exclusive psalmody is to state that hymns and psalms mean the same thing. They are synonyms. Or that one refers to singing with instruments and one without. That argument is not possible to explain away Deuteronomy 31:19,22 where a non-psalm is required to be memorized and sung. Then there is I Corinthians 14:15,26. There I Corinthians talks of singing with the spirit and singing with understanding. This is further enlarged when Paul in verse 26 says “everyone of you has a psalm”. This use of psalm seems to be a song that is outside of the 150 psalms. The criticism is of those who come with a supposed song from the spirit like those who claim to have tongues and prophecies. Those are both assumed to be new word of prophesy and a new word in tongues. Thus, it ought also to be said that they were bringing new psalms not one of the original 150. This was taking place in Christian worship in Corinth that had been set up by Paul and his companions.
If hymn does not mean psalm then this introduces lots of problems for exclusive psalmists. Christ at after the Lord’s Supper sings a “hymn” not a “psalm”. While we might rightly guess that this hymn is a psalm, we cannot scripturally say he sung a psalm. Scripturally he sang a hymn and that is all we know. The same is true for Paul and his companions in prison in Philippi (Acts 16:25). The word used there is again not “psalm”, but rather “hymn”. One can assume that these songs were from The Psalms, but strictly scripturally speaking one cannot say it is. It is only an assumption. The inerrantly chosen word was “hymn”.
This brings up the point of all the times we see people singing non-psalms in the Bible. We have at least:
Luke 1:46-55 (Mary)
Luke 1:67-79 (Zechariah)
Luke 2:14 (the angels)
Luke 2:28-32 (Simeon)
Revelation 5:9f (hosts of heaven)
Exodus 15 (Moses and Miriam)
Deuteronomy 31-32 (Moses)
Judges 5 (Deborah)
Habbakuk 3 (Habbakuk)
And that list does not count many others that are generally considered to early Christological hymns like Colossians 1:15-20. Nor does it count the Song of Solomon, an entire book of the Bible either. The point is that we have more instances of people singing praises to God without the psalter than we do with the psalter in the Bible itself. Now we know how the Jews worshipped from extra-biblical sources, but again the biblical witness needs to carry some weight here. Non-psalms seem acceptable. Now admittedly Dr. Clark makes it possible to sing these songs as they are considered inspired and can be sung, but that attempt falls flat on the previously mentioned Nature of Words Argument. And it also comes into a problem with exactly where is the command to sing only inspired words.
Which brings me to my last point, the idea that the Bible is or contains an approved hymn books is itself an assumption. The idea that the Psalms is the God ordained hymn book is no where in the Bible itself. The application of the Regulative Principle of Worship to say “the psalms are commanded but there is no other command for hymns” makes an assumption in and of itself. Namely that the Psalms was a hymn book. The Regulative Principle does carry the requirement to have a command to do something. But this test is easily applied and passed when we dispense with the assumption that the Psalter is required because it is there. We see commands like Ephesians and Colossians that state “psalms, hymns, and spiritual songs.” We have the command to “sing unto the Lord a new song” (Isaiah). Add this to the many divinely approved examples of non-psalm singing in worship such as those in Revelation 5, then I am quite confident that the demand of the Regulative Principle of worship is met for hymnody.