NOTES for Mar 9:2-13
At the Transfiguration of the Lord, where the disciples saw God's glory and the immaterial Light of Christ, it was Christ's words about the resurrection of the dead that prompted their most interested response. Indeed, is it possible to argue and speak about things that are beyond comprehension? The resurrection of the dead, by contrast, held an important place in Jewish religious consciousness, and so their focus on it is entirely understandable. The evangelist Mark, who makes a point of not entering into detailed explanations of Jewish realities, leaves the substance of the disciples' dispute "offstage." Most likely, they were discussing whether the prophecies about the resurrection should be understood literally or allegorically. In the context of this dispute, it is clear why the disciples began talking about Elijah: if the prophecies about the resurrection are to be understood literally, then it is logical to treat Malachi's prophecy about Elijah's coming in the same way. We should note that the evangelist Luke, and not only he, understands this prophecy allegorically when he speaks of John the Baptist as a prophet "in the spirit and power of Elijah." The disciples have yet another argument in favor of an allegorical interpretation of the prophecy: they have just seen Elijah, together with Moses, speaking with the Lord Jesus. The chief conclusion of the disciples' theological dispute is that different prophecies need to be understood in different ways.
But this is what matters: the Lord Jesus draws the disciples' attention not to the exactness or allegorical nature of the prophecies, but to the way people respond to the actions of God that were foretold. Here the key is not the prophecies about the details of events, but people's rejection of the actions God undertakes for their salvation. Rejection and Christ's Sacrifice on the Cross are the key that the Lord offers the disciples for understanding the prophetic writings, and this is just as important for us.