Verse 4. - And there appeared unto them Elijah with Moses. Moses and Elijah were there because Moses was the lawgiver of the old covenant, and Elijah was conspicuous among the prophets; so that they were the representatives, the one of the Law, and the other of the "goodly fellowship of the prophets. They appear together to bear witness to Christ as the true Messiah, the Savior of the world, prefigured in the Law, and foretold by the prophets. They appear to bear witness to him, and then to resign their offices to the great Lawgiver and Prophet whom they foreshadowed. Then, further, Moses died, but Elijah was translated. Moses, therefore, represents the dead saints who shall rise from their graves and come forth at his coming, while Elijah represents those who shall be found alive at his advent. Our Lord brought with him, at his transfiguration, Moses who had died, and Elijah who had been translated, that he might show his power over both "the quick and the dead." St. Luke 9:31 says that Moses and Elijah "appeared in glory, and spake of his decease (τὴν ἔξοδον αὐτοῦ) which he should accomplish at Jerusalem." They appeared in glory; the Divine splendor irradiated them. They "spake of his decease," literally, his departure - his departure not only out of Jerusalem, but out of this life, by his death upon the cross. The death of Christ was thus shown to be the ultimate end to which the Law and the prophets pointed. Even in that hour of his glory, on the Mount of Transfiguration, this was their theme; and thus the disciples were nerved to look with hope and faith to that which they had contemplated with dismay.

9:1-13 Here is a prediction of the near approach Christ's kingdom. A glimpse of that kingdom was given in the transfiguration of Christ. It is good to be away from the world, and alone with Christ: and how good to be with Christ glorified in heaven with all the saints! But when it is well with us, we are apt not to care for others, and in the fulness of our enjoyments, we forget the many wants of our brethren. God owns Jesus, and accepts him as his beloved Son, and is ready to accept us in him. Therefore we must own and accept him as our beloved Saviour, and must give up ourselves to be ruled by him. Christ does not leave the soul, when joys and comforts leave it. Jesus explained to the disciples the prophecy about Elias. This was very suitable to the ill usage of John Baptist.And there appeared unto them Elias with Moses,.... Or Moses and Elias, as all the Oriental versions read, as in Mat_. 17:3; see Gill on Matthew 17:3,

and they were talking with Jesus; concerning his decease, and what he was to do and suffer at Jerusalem, and of which he himself had lately talked with his disciples; so that this might have been a confirmation of these things to them; See Gill on Matthew 17:3.