And, lo, there appeared to them Moses and Elijah. It is asked, Were Moses and Elijah actually present? or was it only an apparition that was exhibited to the disciples, as the prophets frequently beheld visions of things that were absent? Though the subject admits, as we say, of arguments on both sides, yet I think it more probable that they were actually brought to that place. There is no absurdity in this supposition; for God has bodies and souls in his hand, and can restore the dead to life at his pleasure, whenever he sees it to be necessary. Moses and Elijah did not then rise on their own account, [1] but in order to wait upon Christ. It will next be asked, How came the apostles to know Moses and Elijah, whom they had never seen? The answer is easy. God, who brought them forward, gave also signs and tokens by which they were enabled to know them. It was thus by an extraordinary revelation that they obtained the certain knowledge that they were Moses and Elijah But why did these two appear rather than others who equally belonged to the company of the holy fathers? It was intended to demonstrate that Christ alone is the end of the Law and of the Prophets; and that single reason ought to satisfy us: for it was of the utmost importance to our faith that Christ did not come into our world without a testimony, but with commendations which God had formerly bestowed. I have no objection, however, to the reason which is commonly adduced, that Elijah was selected, in preference to others, as the representative of all the Prophets; because, though he left nothing in writing, yet next to Moses he was the most distinguished of their number, restored the worship of God which had been corrupted, and stood unrivaled in his exertions for vindicating the Law and true godliness, which was at that time almost extinct. And they conversed with Jesus. When they appeared along with Christ, and held conversation with him, this was a declaration of their being agreed. The subject on which they conversed is stated by Luke only: they talked of the decease which awaited Christ at Jerusalem This must not be understood to refer to them as private individuals, but rather to the commission which they had formerly received. Though it was now a long time since they had died and finished the course of their calling, yet our Lord intended once more to ratify by their voice what they had taught during their life, in order to inform us that the same salvation, through the sacrifice of Christ, is held out to us in common with the holy fathers. At the time when the ancient prophets uttered their predictions concerning the death of Christ, he himself, who was the eternal wisdom of God, was sitting on the invisible throne of his glory. Hence it follows that, when he was clothed in flesh, he was not liable to death any farther than as he submitted to it of his own free will.

Footnotes

1 - "Moise et Elie ne sont pas lors ressuscitez pour eux, et pour le regard de la resurrection derniere;" -- "Moses and Elijah did not then rise for themselves, and with respect to the last resurrection."

And behold there appeared unto them Moses and Elias - Moses, a distinguished servant of God, by whom the law was given, and whose institutions typified the Messiah. It was particularly proper that he should appear, when his prophecies and types were about to be fulfilled, and the rites which he had instituted were about to be done away. Elias, or Elijah, a distinguished prophet, taken to heaven without seeing death. See 2-Kings 2:11. Elijah had been honored eminently by being thus translated, and still more by being made the model of the forerunner of the Messiah, Malachi 4:5; Luke 1:17; Matthew 11:14. They appeared "in glory" Luke 9:31; i. e., as they are in heaven with the glory which the redeemed have there.
Talking with him - Luke Luke 9:31 informs us that they conversed about "his decease which he should accomplish at Jerusalem." To redeemed spirits that death was an object of intense interest. By faith in that death they had been saved; and now that the Redeemer of mankind was about to die, it is no wonder that this was the burden of his and their thoughts.
Luke adds Luke 9:32 that "Peter and they that were with him were heavy with sleep." It is not improbable that this was in the night; that Jesus was engaged in prayer; and that he had permitted his weary followers to compose themselves to rest. It was after they were awaked that they saw this vision. Probably the sudden splendor, the bright shining aroused them from sleep.

Moses and Elias - Elijah came from heaven in the same body which he had upon earth, for he was translated, and did not see death, 2-Kings 2:11. And the body of Moses was probably raised again, as a pledge of the resurrection; and as Christ is to come to judge the quick and the dead, for we shall not all die, but all shall be changed, 1-Corinthians 15:51, he probably gave the full representation of this in the person of Moses, who died, and was thus raised to life, (or appeared now as he shall appear when raised from the dead in the last day), and in the person of Elijah, who never tasted death. Both their bodies exhibit the same appearance, to show that the bodies of glorified saints are the same, whether the person had been translated, or whether he had died. It was a constant and prevalent tradition among the Jews, that both Moses and Elijah should appear in the times of the Messiah, and to this very tradition the disciples refer, Matthew 17:10.
We may conceive that the law in the person of Moses, the great Jewish legislator, and the prophets in the person of Elijah, the chief of the prophets, came now to do homage to Jesus Christ, and to render up their authority into his hands; as he was the End of the law, and the grand subject of the predictions of the prophets. This appears more particularly from what St. Luke says, Luke 9:31, that Moses and Elijah conversed with our Lord on his death, which he was about to accomplish, (πληρουν to fulfill), because in it, all the rites, ceremonies, and sacrifices of the law, as well as the predictions of the prophets, were fulfilled.

And behold there appeared unto them,.... The disciples:
Moses and Elias; Moses the giver of the law, and Elias one of the chief of the prophets: one of them had been dead near a thousand and five hundred years, and the other had been caught up to heaven, about nine hundred years before this. The Jews sometimes speak of these two as together. They say (c),
"that the Shekinah never descends below, but , "Moses and Elias" ascend above.''
Yea, they expect that these two will come together in future time; for so they represent (d) a God saying to Moses;
"Moses, as thou hast given thy life for them (the Israelites) in this world, so in time to come (the days of the Messiah) when I shall bring Elias the prophet, , "you two shall come together".''
Now they came. Luke says, they appeared "in glory": in glorious bodies, in a glory upon their bodies; like, though inferior, to the glorious body of Christ, now transfigured: that they appeared in their own real bodies, no doubt need be made; about the body of Elijah, or Elias, there is no difficulty; since he was carried soul and body to heaven, he died not, but was changed; and has ever since remained in a glorious body, in which he doubtless now appeared: and why this should not be the case of Moses, or why he should appear in another body, and not his own, I see not; for though he died, yet he was buried by the Lord, and no man ever knew the place of his sepulchre; and there was a dispute about his body, between Michael and the devil, all which are uncommon circumstances: so that it might be, that his body was, quickly after his death, raised and restored to him; or at this time, as a pledge of the resurrection of the dead, as Christ's transfiguration was of his glory. The Jews have a notion that Moses is not dead, but is ascended, and stands and ministers to God, in the highest heavens (e): the appearance of these two with Christ, was to show, that Christ is the end of the law and prophets; that there is an entire agreement between him and them, and that they have their full accomplishment in him; and also shows, that he was neither Elias, nor any of the prophets, as some took him to be; since he was distinct from them, and the chief and more glorious than any of them. If it should be asked; how came the disciples to know these two to be Moses and Elias, since they never saw them before, nor could have any statues or pictures of them, these being not allowed among the Jews; nor do the accounts of them in Scripture seem to be sufficient to direct them to such a thought; especially, since by their glorification, they must be greatly altered: it may be replied, they knew them, either by immediate divine revelation, or by the discourse that passed between them and Christ; for it follows,
talking with him. The Jews often speak of the appearance of Elias to their doctors, and of his conversing with them, and teaching them. Whether this is done with design to lessen the glory of this appearance, I will not say; however, they cannot reasonably object to the probability of this account, since they make it to be so frequent among themselves; though they look upon it as an high favour, and that such are holy good men, that are indulged with it, take an instance or two: thus they say (f) of a certain person,
"Lo! the pious man, whom Elias used , "to converse with".''
And elsewhere it is said (g),
"R. Phineas and R. Mari, the sons of R. Chasda, were godly men, , "and Elias was talking with them", and they were priests.''
What Moses and Elias were talking with our Lord about, is expressed by Luke; see Gill on Luke 9:31.
(c) T. Bab. Succab, fol. 5. 1. (d) Debarim Rabba, sect. 3. fol. 239. 2. (e) T. Bab. Sota, fol. 13. 2. Maimon. praefat. ad Seder Zeraim in Talmud. fol. 86. 4. (f) T. Bab. Bava Bathra, fol. 7. 2. (g) Juchasin, fol. 101. 1. Vid. fol. 79. 1. & 118. 2. & 13. 132. 1. & T. Bab. Cetubot, fol. 106. 1.

There appeared unto them Moses and Elias. (1) Among all the prophets and saints of the Old Testament these were the two, of which one had not died (2-Kings 2:11), and the other had no sooner tasted of death than his body was withdrawn from under the dominion of death and of him that had the power of death (Deuteronomy 34:6; Jude 9). Both, therefore, came from hades, but from hades conquered. (2) Again, these two were the acknowledged heads and representatives, the one of the law, the other of the prophets (compare Matthew 7:12).
And they were talking with Jesus. The subject of their conversation is given in Luke 9:31. It was the decease (exodus, departure, referring to his death and ascension) which he should accomplish at Jerusalem. In this brief interview between the greatest worthies of the old dispensation and the Founder of the new dispensation their conversation would be confined to the most important theme of earth and heaven. That was the Savior's death.

There appeared Moses and Elijah - Here for the full confirmation of their faith in Jesus, Moses, the giver of the law, Elijah, the most zealous of all the prophets, and God speaking from heaven, all bore witness to him.