This collection of 150 Psalms, whenever precisely it may have been made, was divided into five books, each ending with an outburst of praise to the God of Israel.[4] The key to this somewhat artificial arrangement is no doubt to be found in the desire to make the Psalter correspond with the Pentateuch. "Moses," says a Rabbinical commentator (Midrash _Tillim_), "gave five-fifths of the Law, and correspondingly David gave the book of _Tehillim_, in which are five books." Of this Dr. Cheyne says, "The remark is a suggestive one: it seems to mean this--that the praise-book is the answer of the worshipping community to the demands made by its Lord in the Law, the reflexion of the external standard of faith and obedience in the utterance of the believing heart." This criticism is so illuminating that it may well suggest the first great principle in our own Christian use of the Psalter. I. The Psalter is the inspired answer of praise which human faith is privileged to make to {8} God's revelation. It is the "new song" put in the mouth of humanity by its Creator. "Thou preparest their heart, and Thine ear hearkeneth thereto" (Ps. x. 19). This is surely a very great thought. The Old Testament is the record of God's gradual unveiling of Himself to His elect, whom for the world's sake He had chosen out of the world. The revelation was not indeed to them alone. God had spoken in many ways, more than even the Church yet recognises, to the heathen world. Yet to Israel God gave that highest privilege of receiving and keeping the true knowledge of Himself, of His unity, His universality, His moral being, His holiness, His love, and of the demand which this knowledge makes on human conscience. The unknown author of 2 Esdras, looking back on history after the great blow had fallen on Jerusalem, has expressed this in vivid and pathetic language: "Of all the flowers of the world Thou hast chosen Thee one lily: and of all the depths of the sea Thou hast filled Thee one river: and of all builded cities Thou hast hallowed Sion unto Thyself: ... and among all the multitudes of peoples Thou hast gotten Thee one people: and unto this people, whom Thou lovedst, Thou gavest a law that is approved of all" (2 Esd. v. 24-7). In the Psalter God {9} has provided, as it were, for His people the words of praise in which their thankful hearts may express their love and loyalty to what He has revealed. This feature, the glad response to revelation, is stamped upon the Psalter from end to end. Thus the 1st Psalm describes the secret of human blessedness: His delight is in the law of the Lord: And in His law will he exercise himself day and night.