George Haydock's Catholic Bible Commentary - Mark 9:4
The law and the prophets were signified by Moses and Elias; both bear testimony to the divinity of Jesus Christ's mission, which was effectually to close the old, and open the new dispensation. By the apparitions of these two illustrious personages, we learn also that sometimes, though not often, there is, by the permission of heaven, a certain intercourse between the living and the dead. (Bristow) read more
Hawker's Poor Man's Commentary - Mark 9:2-13
(2) And after six days Jesus taketh with him Peter, and James, and John, and leadeth them up into an high mountain apart by themselves: and he was transfigured before them. (3) And his raiment became shining, exceeding white as snow; so as no fuller on earth can white them. (4) And there appeared, unto them Elias with Moses: and they were talking with Jesus. (5) And Peter answered and said to Jesus, Master, it is good for us to be here: and let us make three tabernacles; one for thee, and one... read more