Puritan Board Senior
Except that, again, the "new" that is referenced in a particular psalm speaks of itself as it is a "new" psalm as it's being written. That's the immediate context of the term "new" as it is used in the Book of Psalms.So, in context, we, the NT, new covenant church, are commanded to be taught by the Psalms. The Psalms command that we sing a new song. So, just as preaching and praying may have "uninspired" yet regulated content, so may our song.
Certainly there is an aspect that we sing new Psalms, but that aspect is in singing the Psalms in light of the NT, having the full revelation of God to make our understanding of the Psalms more complete. Therefore we sing them anew because we sing them according to the New Covenant dispensation.