The first step on St. Hilary’s path of sound method of knowledge and reason is to demonstrate how the First Psalm cannot be spoken by Christ nor that He is the subject of the First Psalm:
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 hath 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 spake He in parables that the saying might be fulfilled: I will open My mouth in parables.” The Lord then gave fulfilment in act to His own prophecy, speaking in the parables in which He had promised that He would speak.
Note the the “sound method” St. Hilary uses, while typical of the Fathers, is not very popular among many modern biblical scholars. The tendency today would be to read the First Psalm in isolation of the rest of Scripture. The justification for this is to maintain the original intent and context of the author. Since (as St. Hilary himself admits) the Psalms (and the rest of Scripture) are written by a variety of authors, each particular part needs to be isolated from the rest in order to properly understand it.
St. Hilary, however, has no qualms about juxtaposing different parts of Scripture in order to reach a deeper understanding. In this case, he uses both Psalm 78:1 (LXX — 77:1 in the Mesoretic)* and Matthew 13:35 to demonstrate that Christ is the Lord of the Law, and therefore cannot be the one whose happiness is in bending his will to the Law. How can Christ’s happiness be dependent upon something that is already His?
*When dealing with the Psalms as quoted by the Fathers, things can be a bit confusing because the Septuagint (LXX) numbers the Psalms differently than the Mesoretic Text, which forms the basis for almost all modern English translations. For this reason, there will often be two different numbers given to refer to the same verse. In future I will give the LXX number first followed by a slash and then the Mesoretic number. For example, today’s reference would be written: Psalm 78:1/77:1