Gregory the Great — as excerpted in the Catena Aurea on Mark 9:1-8

“(Mor. 32, 6) Because, in the height of the brightness of heaven above, they who shine in righteousness of life, will cling to Him; for by the name of garments, He means the just whom He joins to Himself. There follows, And there appeared unto them Elias with Moses, and they were talking with Jesus.”