God is the author of the Psalms, through the Holy Spirit’s work of inspiration, guiding the human authors to write what He intended, as we read in 2 Peter 1:20-21 … “knowing this first of all, that no prophecy of Scripture comes from someone’s own interpretation. For no prophecy was ever produced by the will of man, but men spoke from God as they were carried along by the Holy Spirit.” And in addition to that, through divine providence He is also the arranger of the contents of the Psalms. It is by His design that the collection of 150 Psalms is divided into five groups, with chapters 1-2 serving as an introduction. The rest of psalms are arranged as Book 1 (3-41), Book 2 (42-72), Book 3 (73-89), Book 4 (90-106), and Book 5 (107-150). And each book concludes with some kind of doxology.
And it is also by His design that Psalms 1 and 150 are placed where they are, as an introduction and conclusion to the whole collection. Our praises begin by acknowledging that the only path to blessing is that which honors the Lord by loving and walking in accord with His Word. Doing so will insure that we will eternally enjoy the favor of the Lord. And our praises end with the jubilant praise in His presence that will last into eternity, praise that is supported by glorious music from every kind of musical instrument, indeed, from everything that has breath! All of the Psalms, like all of scripture, are ultimately Messianic, in part, because Jesus not only sang all these Psalms in His day in Israel, but as God, He actually wrote them!