(13) Then the disciples understood.--The words are suggestive both as indicating the conclusion in which they ultimately rested, and the frankness with which they owned how slowly they had passed from the literalism of the scribes to a true apprehension of the spiritual meaning of the prophecy in question.

Verse 13. - Then the disciples understood. Though Jesus had said publicly concerning John, "This is he of whom it is written, Behold, I send my messenger before thy face," and, "This is Elias which was for to come" (Matthew 11:10, 14); and though the angel Gabriel, in announcing his birth, had avowed that he should "go before the Christ in the spirit and power of Elias" (Luke 1:17), the apostles hitherto had not taken to heart the truth thus conveyed. Indeed, it was something quite new that they should thus at once apprehend Christ's meaning, so slow were they of faith, so unintelligent in appreciating the full signification of their Master's instructions.

17:1-13 Now the disciples beheld somewhat of Christ's glory, as of the only begotten of the Father. It was intended to support their faith, when they would have to witness his crucifixion; and would give them an idea of the glory prepared for them, when changed by his power and made like him. The apostles were overcome by the glorious sight. Peter thought that it was most desirable to continue there, and to go no more down to meet the sufferings of which he was so unwilling to hear. In this he knew not what he said. We are wrong, if we look for a heaven here upon earth. Whatever tabernacles we propose to make for ourselves in this world, we must always remember to ask Christ's leave. That sacrifice was not yet offered, without which the souls of sinful men could not have been saved; and important services were to be done by Peter and his brethren. While Peter spoke, a bright cloud overshadowed them, an emblem of the Divine presence and glory. Ever since man sinned, and heard God's voice in the garden, unusual appearances of God have been terrible to man. They fell prostrate to the earth, till Jesus encouraged them; when looking round, they beheld only their Lord as they commonly saw him. We must pass through varied experiences in our way to glory; and when we return to the world after an ordinance, it must be our care to take Christ with us, and then it may be our comfort that he is with us.Then the disciples understood,.... By his saying that Elias was come, and by the account he gave of his ill usage, it was clear to them,

that he spake unto them of John the Baptist; and that he was the Elias that was to come, and was come: so that this observation, that according to prophecy Elias was to come before the Messiah, was no objection to Jesus being the Messiah; but on the contrary, since he that was intended by Elias was come, and had done his work and office, it was a confirmation of the truth of his Messiahship.