Luke 9:30

The mystery, namely, of His incarnation, also the life-giving Passion accomplished on the sacred cross.

(ut sup. 13.) But while these things were so, that it might be shown there was but one Lord of the new and old covenant, and the mouths of heretics might be shut, and men might believe on the resurrection, and He also, who was transfigured, be believed to be the Lord of the living and the dead, Moses and Elias, as servants, stand by their Lord in His glory; hence it follows, And behold there talked with him two men. For it became men, seeing the glory and confidence of their fellow servants, to admire indeed the merciful condescension of the Lord, but to emulate those who had laboured before them, and looking to the pleasantness of future blessings, to be the more strengthened for conflicts. For he who has known the reward of his labours, will the more easily endure them.

Or else, according to your capacity is the word either lessened or increased to you, and unless you ascend the summit of a higher wisdom, you behold not what glory there is in the word of God. Now the garments of the Word, are the discourses of the Scriptures, and certain clothings of the Divine mind; and as His raiment shone white, so in the eyes of your understanding, the sense of the divine words becomes clear. Hence after Moses, Elias; that is, the Law and the Prophets in the Word. For neither can the Law exist without the Word, nor the Prophet, unless he prophesied of the Son of God.