What follows is the opening paragraph of St. Hilary’s homily on the First Psalm. Unfortunately it is rather lengthy, but bear with him. Pay special attention to the first sentence:
The primary condition of knowledge for reading the Psalms is the ability to see as whose mouthpiece we are to regard the Psalmist as speaking, and who it is that he addresses. For they are not all of the same uniform character, but of different authorship and different types. For we constantly find that the Person of God the Father is being set before us, as in that passage of the eighty-eighth Psalm: ‘I have exalted one chosen out of My people, I have found David My servant, with My holy oil have I anointed him. He shall call Me, Thou art my Father and the upholder of my salvation. And I will make him My first-born, higher than the kings of the earth’; while in what we might call the majority of Psalms the Person of the Son is introduced, as in the seventeenth: ‘A people whom I have not known hath served Me’; and in the twenty-first: ‘they parted My garments among them and cast lots upon My vesture.’ But the contents of the first Psalm forbid us to understand it either of the Person of the Father or of the Son: ‘But his will hath been in the law of the Lord, and in His Law will he meditate day and night.’ Now in the Psalm in which we said the Person of the Father is intended, the terms used are exactly appropriate, for instance: ‘He shall call Me, Thou art my Father, my God and the upholder of my salvation’; and in that one in which we hear the Son speaking, He proclaims Himself to be the author of the words by the very expressions He employs, saying, ‘A people whom I have not known hath served Me.’ That is to say, when the Father on the one hand says: ‘He shall call Me’; and the Son on the other hand says: ‘a people hath served Me,’ they shew that it is They Themselves Who are speaking concerning Themselves. Here, however, where we have ‘But his will hath been in the Law of the Lord’; obviously it is not the Person of the Lord speaking concerning Himself, but the person of another, extolling the happiness of that man whose will is in the Law of the Lord. Here, then, we are to recognise the person of the Prophet by whose lips the Holy Spirit speaks, raising us by the instrumentality of his lips to the knowledge of a spiritual mystery.
Who is saying these words? To whom are they addressed? These questions are not only important to an understanding of the Psalms, but to Scripture as a whole. Note also that St. Hilary understands that the primary speakers within the Psalms are God the Father and God the Son. In others words, (just as it is so in the rest of Scripture), God is revealing to us who He is through the Psalms. They help us answer that most important question: Who is God?
What makes the First Psalm so interesting, however, is that it is neither the Father or the Son who are speaking. As such, this Psalm, in particular, should pique our interest — especially since it does come first in the Psaltery.