SEV Biblia, Chapter 17:13
Los discípulos entonces entendieron, que les habl de Juan el Bautista.
Clarke's Bible Commentary - Matthew 17:13
Verse 13. Then the disciples understood] When he spoke of the sufferings of this prophetic Elijah, and also of his own, which had been the subject of the conversation on the mount, during the transfiguration, they clearly apprehended that he spoke of John the Baptist.
John Gill's Bible Commentary
Ver. 13. Then the disciples understood , etc.] 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.
Matthew Henry Commentary
Verses 1-13 - Now the disciples beheld somewhat of Christ's glory, as of the onl begotten of the Father. It was intended to support their faith, when they would have to witness his crucifixion; and would give them an ide of the glory prepared for them, when changed by his power and made lik him. The apostles were overcome by the glorious sight. Peter though 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 upo earth. Whatever tabernacles we propose to make for ourselves in thi world, we must always remember to ask Christ's leave. That sacrific was not yet offered, without which the souls of sinful men could no have been saved; and important services were to be done by Peter an his brethren. While Peter spoke, a bright cloud overshadowed them, a emblem of the Divine presence and glory. Ever since man sinned, an heard God's voice in the garden, unusual appearances of God have bee terrible to man. They fell prostrate to the earth, till Jesu encouraged them; when looking round, they beheld only their Lord a they commonly saw him. We must pass through varied experiences in ou 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 comfor that he is with us.
Greek Textus Receptus
τοτε 5119 ADV συνηκαν 4920 5656 V-AAI-3P οι 3588 T-NPM μαθηται 3101 N-NPM οτι 3754 CONJ περι 4012 PREP ιωαννου 2491 N-GSM του 3588 T-GSM βαπτιστου 910 N-GSM ειπεν 2036 5627 V-2AAI-3S αυτοις 846 P-DPM
Robertson's NT Word Studies
17:13 {qen understood} (tote sunekan). One of the three k aorists. It was plain enough even for them. John was Elijah in spirit and had prepared the way for the Messiah.