As [Jesus] was praying, the appearance of his face changed, and his clothes became as bright as a flash of lightning. Two men, Moses [representing the Law] and Elijah [representing the Prophets], appeared in glorious splendor, talking with Jesus. They spoke about his departure, which he was about to bring to fulfillment at Jerusalem ... a cloud appeared and covered them, and [Peter, James, and John] were afraid as they entered the cloud. A voice came from the cloud, saying, “This is my Son, whom I have chosen; listen to him.” When the voice had spoken, they found that Jesus was alone. (Lk.9:29-36)My friend zeroed in on the way Jesus now stood there alone, embodying in His Life and Person all that Moses and Elijah had revealed in part. My friend was absolutely right. But there's another side of the equation.
The voice, a manifestation of God the Father, and the cloud, a visual representation of the Holy Spirit, also give way to Jesus standing alone before the apostles. The thirty-something year old man standing before them speaks the words of the Father, and He is the conduit through which the Holy Spirit is poured out upon the world! "[Jesus] is the image of the invisible God ... in him all the fulness of God was pleased to dwell" (Col.1:15,19). The Transfiguration says all of this. Turning to the Epistle to the Hebrews, the first verses read like a theological commentary on this event:
In the past God spoke to our ancestors through the prophets at many times and in various ways, but in these last days he has spoken to us by his Son, whom he appointed heir of all things, and through whom also he made the universe. The Son is the radiance of God’s glory and the exact representation of his being, sustaining all things by his powerful word. (Heb.1:1-3)And so long as I'm quoting those verses from Hebrews, let me quote St. John of the Cross:
In giving us his Son, his only Word (for he possesses no other), he spoke everything to us at one in this sole Word - and he has no more to say ... because what was spoken before to the prophets in parts, he has now spoken all at once by giving us the All Who is His Son. (CCC 65)