“Then the disciples understood that he spake unto them of John the Baptist.”
Matthew 17:13 — Greek Interlinear
Church Fathers on Matthew 17:13
It was a tradition of the Pharisees following the Prophet Malachi, that Elias should come before the coming of the Saviour, and bring back the heart of the fathers to the children, and the children to the fathers, and restore all things to their ancient state. The disciples then consider that this transformation which they had seen in the mount was His coming in glory, and therefore it is said, 'And his disciples asked him, saying, How then say the Scribes that Elias must…
The disciples knew not of the coming of Elias out of the Scriptures; but the Scribes made it known to them; and this report was current among the ignorant multitude, as was that concerning Christ. Yet the Scribes did not explain the coming of Christ and of Elias, as they ought to have done. For the Scriptures speak of two comings of Christ; that which has taken place, and that which is yet to be. But the Scribes, blinding the people, spake to them only of His second coming,…
Or; 'He shall restore all things,' that is those whom the persecution of Antichrist shall have overthrown; as He Himself should restore by His death those whore He ought.