The Christian use of the Psalter is as old as Christianity itself. The new-born Catholic Church, returning from her earliest conflict with the kingdoms of this world, found the most natural expression of her faith and her need in the words of the 2nd Psalm: Why did the Gentiles rage, And the peoples imagine vain things? The kings of the earth set themselves in array, And the rulers were gathered together, Against the Lord, and against His Anointed. (Acts iv. 25, 26, R.V.) {2} Before this, on the very birthday of the Church, the chief of the Apostles had appealed to the witness of "David," for the Resurrection and Triumph of the Holy One (Pss. xvi., cx. in Acts ii. 25-8, 34, 35). And even earlier, during the ten days of waiting, the great Psalms of righteous wrath (thought so impossible by many to-day) had supplied the prophecy of the fall of Judas: Let his habitation be made desolate, And let no man dwell therein; and the justification of the election of Matthias: His office let another take. (Pss. lxix. and cix. in Acts i. 20.) So harmoniously did the praise-book of the Jewish Church pass into the service of Christ; so clearly did the first believers recognise that the Spirit of Christ was the same Who had spoken by "David." This immediate appropriation of the Psalter as a book of Christian witness is remarkable evidence to the felt unity and continuity of the two Covenants. No book of the Old Testament, with the exception of Isaiah, is so frequently quoted in the New as the book of Psalms. But still more remarkable is the influence of the Psalter on Christian _worship_. The Church {3} exists in the world not only as the teaching, but also as the worshipping community. As the ages pass she ceases not to bear the witness of her praise and thanksgiving to the Father, the Son, and the Holy Ghost. From the beginning she showed a tendency to do this in ordered and liturgical forms. The Apostolic Church continued steadfast in "the prayers" (Acts ii. 42, R.V.). The expression implies not merely a daily gathering for worship, but the offering of that worship in a fixed and orderly manner, suggested, no doubt, by the existing Jewish services. Whatever may have been the actual form of "the prayers" in the first age of the Church, or whatever stages they may have passed through, there can be no doubt that they are the germ of all the rich later developments of the liturgy of the Church, such as are represented in the Middle Ages by the Missal and the Breviary, and to-day by our own Book of Common Prayer.