Having established that Christ is not the speaker or the subject of Psalm 1, and that the Prophet is the speaker, St. Hilary finally gives us the subject of the Psalm:

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 fulfilment of all righteousness. That this is the necessary interpretation will be shewn as the exposition of the Psalm proceeds.

In other words, we are the subject of Psalm 1 — we who desire to walk the Christian walk; who desire to fulfill the image and likeness with which we have been endowed; we who desire to bring our Lord, God and Savior into our lives so that we might share in His body — a body that gives us access to His Kingdom and His eternity.