5 It proceeds: “I speak of the things which I have made unto the King.” Is the Father still speaking? If the Father is still speaking, let us enquire how this also can be understood by us, consistently with the true Catholic Faith, “I speak of the things that I have made unto the King.” For if it is the Father speaking of His own works to His Son, our “King,” what works is the Father to speak of to the Son, seeing that all the Father's works were made by the Son's agency?
Or, in the words, “I speak of My works unto the King,” does the word, “I speak,” itself signify the generation of the Son? I fear whether this can ever be made intelligible to those slow of comprehension: I will nevertheless say it. Let those who can follow me, do so: lest if it were left unsaid, even those who can follow should not be able. We have read where it is said in another Psalm, “God has spoken once.” So often has He spoken by the Prophets, so often by the Apostles, and in these days by His Saints, and does He say, “God has spoken once”?
How can He have spoken but “once,” except with reference to His “Word”? But as the “Mine heart has uttered a good Word,” was understood by us in the other clause of the generation of the Son, it seems that a kind of repetition is made in the following sentence, so that the “Mine heart has uttered a good Word,” which had been already said, is repeated in what He is now saying, “I speak.” For what does “I speak” mean? “I utter a Word.” And whence but from His heart, from His very inmost, does God utter the Word?
You yourself do not speak anything but what you bring forth from your “heart,” this word of yours which sounds once and passes away, is brought forth from no other place: and do you wonder that God “speaks” in this manner? But God's “speaking” is eternal. You are speaking something at the present moment, because you were silent before: or, look you, you have not yet brought forth your word; but when you have begun to bring it forth, you as it were “break silence;” and bring into being a word, that did not exist before.
It was not so God begot the “Word.” God's “speaking” is without beginning, and without end: and yet the “Word” He utters is but “One.” Let Him utter another, if what He has spoken shall have passed away. But since He by whom it is uttered abides, and That which is uttered abides; and is uttered but once, and has no end, that very “once” too is said without beginning, and there is no second speaking, because that which is said once, does not pass away. The words “Mine heart has uttered a good Word,” then, are the same thing with, “I speak of the things which I have made unto the King.”
Why then, “I speak of the things which I have made”? Because in the Word Itself are all the works of God. For whatever God designed to make in the creation already existed in “the Word;” and would not exist in the reality, had it not existed in the Word, just as with you the thing would not exist in the building, had it not existed in your design: even as it is said in the Gospel: “That which was made in Him was life.” That which was made then was in existence; but it had its existence in the Word: and all the works of God existed there, and yet were not as yet “works.”
“The Word” however already was, as this “Word was God, and was with God:” and was the Son of God, and One God with the Father. “I speak of the things I have made unto the King.” Let him hear Him “speaking,” who apprehends “the Word:” and let him see together with the Father the Everlasting Word; in whom exist even those things that are yet to come: in whom even those things that are past have not passed away. These “works” of God are in “the Word,” as in the Word, as in the Only-Begotten, as in the “Word of God.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)