And as he says this we must inquire concerning what man we are to understand him to be speaking. He says: Happy is the man who has not walked in the counsel of the ungodly nor stood in the way of sinners, and has not sat in the seat of pestilence. But his will has been in the Law of the Lord, and in His Law will he meditate day and night. And he shall be like a tree planted by the rills of water, that will yield its fruit in its own season. His leaf also shall not wither, and all things, whatsoever he shall do, shall prosper. I have discovered, either from personal conversation or from their letters and writings, that the opinion of many men about this Psalm is, that we ought to understand it to be a description of our Lord Jesus Christ, and that it is His happiness which is extolled in the verses following. But this interpretation is wrong both in method and reasoning, though doubtless it is inspired by a pious tendency of thought, since the whole of the Psalter is to be referred to Him: the time and place in His life to which this passage refers must be ascertained by the sound method of knowledge guided by reason.

Now the words which stand at the beginning of the Psalm are quite unsuited to the Person and Dignity of the Son, while the whole contents are in themselves a condemnation of the careless haste that would use them to extol Him. For when it is said, and his will has been in the Law of the Lord, how (seeing that the Law was given by the Son of God) can a happiness which depends on his will being in the Law of the Lord be attributed to Him Who is Himself Lord of the Law? That the Law is His He Himself declares in the seventy-seventh Psalm, where He says: Hear My Law, O My people: incline your ears unto the words of My mouth. I will open My mouth in a parable. And the Evangelist Matthew further asserts that these words were spoken by the Son, when he says For this cause spoke He in parables that the saying might be fulfilled: I will open My mouth in parables. The Lord then gave fulfillment in act to His own prophecy, speaking in the parables in which He had promised that He would speak. But how can the sentence, and he shall be like a tree planted by the rills of water, —” wherein growth in happiness is set forth in a figure —” be possibly applied to His Person, and a tree be said to be more happy than the Son of God, and the cause of His happiness, which would be the case if an analogy were established between Him and it in respect of growth towards happiness? Again, since according to Wisdom and the Apostle, He is both before the ages and before times eternal, and is the First-born of every creature; and since in Him and through Him all things were created, how can He be happy by becoming like objects created by Himself? For neither does the power of the Creator need for its exaltation comparison with any creature, nor does the immemorial age of the First-born allow of a comparison involving unsuitable conditions of time, as would be the case if He were compared to a tree. For that which shall be at some point of future time cannot be looked upon as having either previously existed or as now existing anywhere. But whatsoever already is does not need any extension of time to begin existence, because it already possesses continuous existence from the date of its beginning up till the present.

And so, since these words are understood to be inapplicable to the divinity of the Only-begotten Son of God, our Lord Jesus Christ, we must suppose him, who is here extolled as happy by the Prophet, to be the man who strives to conform himself to that body which the Lord assumed and in which He was born as man, by zeal for justice and perfect fulfillment of all righteousness. That this is the necessary interpretation will be shown as the exposition of the Psalm proceeds. — On Psalm 1.

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, You are 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 has 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 has 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, You are 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 has 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 has served Me, they show that it is They Themselves Who are speaking concerning Themselves. Here, however, where we have But his will has 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 recognize 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. — On Psalm 1