The Psalms are for Christians!

"It hath been pretended, that the language and manner of these Psalms are not suited to the spiritual nature of our Gospel-worship. That, however, may as well be urged against the reading of them, as against the singing of them: nay, against the reading of a great part of the Old Testament in our Christian worship. It is certain, many passages in the Book of Psalms, or of other Scripture songs, are expressive of the exercises of faith, repentance, love, or the like graces, which still remain of the same form as under the Old Testament. The predictions are either accomplished, and so may be sung to the honour of God's mercy and faithfulness; or, if not accomplished, may be sung in the hopes that God will accomplish them in his time. The history of what God did for his Jewish servants and church, may be sung with admiration of his love, wisdom, power, and grace therein manifested. It is further to be considered, that much of what related to David, or the Jewish church, was typical of the character and concerns of Jesus Christ, and of the Gospel church; and so ought to be sung with a special application thereto." John Brown, Preface to The Psalms of David in Metre