He charged them that they should tell no man what things they had seen, save when the Son of man should have risen again from the dead. They were not even to tell their fellow-disciples, lest it might cause vexation or envy that they had not been thus favored. The time of our Lord's resurrection would be a fitting opportunity for revealing this mystery; and then the disciples would understand and believe it, when, after his passion and death, which were an offense to them, they should see him rising in glory, of which event the Transfiguration was a type. For, by the Resurrection they would certainly know that Christ underwent the death of the cross, not by constraint, but of his own accord, and out of his great love for us.
Questioning among themselves what the rising again from the dead should mean; that is, his own rising from the dead, of which our Lord had just been speaking. No doubt the general resurrection at the end of the world was an article of faith with which the disciples were familiar. But they could not understand, when he spake of his own immediate rising from the dead. So their perplexities led them at last to ask him the question; or rather to make the remark to him, The scribes say that Elijah must first come; with a view to obtaining some clearer understanding. They had just seen Elijah in the Transfiguration, and they had seen him disappear. They wondered why he should have departed. They thought, it may be, that he ought to have remained, that he might be the forerunner of Christ and of his kingdom and glory, according to the prophecy of Malachi (Malachi 4:6). This the scribes taught; but they erred in the confusion of times, for they did not distinguish the first coming of Christ in the flesh from his second advent to judgment. The thought upon the mind of the disciples appears to have been this: They heard Christ speak of his own resurrection as close at hand, and they had seen the type of it in his transfiguration; and they thought that immediately after that, Christ's kingdom would come, and he would reign gloriously. Why, then, had not Elijah remained, that he might be his precursor? St. Matthew (Matthew 17:13) tells us that our Lord's words which follow showed the disciples that when he said that Elijah was to come first and restore all things, he meant them to understand" that he spake unto them of John the Baptist." Upon the question of a future coming of Elijah, it seems safest to confess our ignorance. The prophecy of Malachi was no doubt in part fulfilled in the coming of John the Baptist; but it would be rash to affirm that it may not receive another and more literal fulfillment before the second advent. A host of ancient Christian expositors have held that Elijah will appear in person before the second advent of Christ. St. Augustine, in his 'City of God' (20:29), says, "Not without reason do we hope that before the coming of our Judge and Savior Elias will come, because we have good reason to believe that he is now alive; for, as Holy Scripture distinctly informs us, he gas taken up from this life in a chariot of fire. When, therefore, he is come he shall give a spiritual explanation of the Law which the Jews at present understand carnally, and will turn the hearts of the fathers to the children, and the children to the fathers; that is, the Jews who are the children will understand the Law in the same sense as their fathers the prophets understood it." Indeed, this is one of the principal reasons assigned by the Fathers for this appearance of Elijah, that he may convert the Jews.