The Lord of both old and new
At the time of the Transfiguration the witness given to the Son was confirmed by both the voice of the Father and by Moses and Elijah, who appeared beside Jesus as his servants. The prophets are looking at Peter, James and John the apostles; the apostles behold the prophets. In one and the same place the princes of the old covenant come together with those of the new. Holy Moses saw Peter the holy one; the shepherd chosen by the Father saw the shepherd chosen by the Son. The former had rebuked the sea in days of old that God’s people might pass through the midst of its waves, the latter suggested setting up a tent to shelter the Church. The chaste man of the Old Testament saw the chaste man of the New: Elijah could see John. He who was lifted up in a chariot of fire saw him who rested on the breast of the Fire (Jn 13,23). And then the mountain became the symbol of the Church: at its summit Jesus unifies the two Testaments that this Church gathers up. He made it known that he is Lord of the one as of the other, of the Old which received his mysteries, of the New which revealed the glory of his actions.
St. Elizabeth Ann Seton