Gregory the Great — as excerpted in the Catena Aurea on Luke 24:13-24

“(23. in Ev.) Rightly also He refrained from manifesting to them a form which they might recognise, doing that outwardly in the eyes of the body, which was done by themselves inwardly in the eyes of the mind. For they in themselves inwardly both loved and doubted. Therefore to them as they talked of Him He exhibited His presence, but as they doubted of Him He concealed the appearance which they knew. He indeed conversed with them, for it follows, And he said to them, What manner of communications, &c.”