The psalms look forward, they speak of the promise. Isaac Watts wrote in relation to the psalms 'where the original runs in form of prohecy concerning Christ and his salvation, it is not necessary that we should sing in the style of prediction when the things foretold are brought into open light by full accomplishment.'
Don't get me wrong the psalms are great. I love singing them, but if the Jews were not limited to them why should we be? Isn't it good to sing of redemption accomplished, Christ risen as things that have happened. If we will sing a new song (rev 5:9) in heaven, whats wrong with singing a new song here and now?
Jonathan (Pastor, Salem Baptist, Cambs, UK. Grace Baptist [BCF 1689])
"After all, there is a Protestantism still worth contending for, there is a Calvinism still worth proclaiming, and a gospel well worth dying for" - C H Spurgeon
"As we are knit to Christ by faith, so we must be knit to the communion of saints by love" - R Sibbes
"A man's 'free'-will cannot cure him even of the tooth ache, or of a sore finger; and yet he madly thinks it is in its power to cure his soul." -Augustus Toplady