6 And the disciples hearing, fell upon their face, and were very much afraid.
Remigius: Whereas the holy Apostles fell upon their faces, that was a proof of their sanctity, for the saints are always described to fall upon their faces, but the wicked to fall backwards. [Gen 49, 17; Isa 28, 13; John 18, 6]
7 And Jesus came and touched them: and said to them, Arise, and fear not.
Jerome: And whereas they were laid down, and could not raise themselves again, He approaches them, touches them gently, that by His touch their fear might be banished, and their unnerved limbs gain strength. . . . He first banishes their fear, that He may after impart teaching.
8 And they lifting up their eyes saw no one but only Jesus.
Jerome: Had Moses and Elias continued with the Lord, it might have seemed uncertain to which in particular the witness of the Father was borne. Also they see Jesus standing after the cloud has been removed, and Moses and Elias disappeared, because after the shadow of the Law and Prophets has departed, both are found in the Gospel.
9 And as they came down from the mountain, Jesus charged them, saying: Tell the vision to no man, till the Son of man be risen from the dead.
Jerome: He will not be preached among the people, lest the marvel of the thing should seem incredible, and lest the cross following after so great glory should cause offence.
Remigius: If His majesty should be published among the people, they should hinder the dispensation of His passion, by resistance to the chief Priests; and thus the redemption of the human race should suffer impediment.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. I (London: Rivington, 1842).