John Chrysostom
Catena Aurea · Markusevangelium 9
And as they came down from the mountain, he charged them that they should tell no man what things they had seen, till the Son of man were risen from the dead. And they kept that saying with themselves, questioning one with another what the rising from the dead should mean. And they asked him, saying, Why say the Scribes that Elias must first come? And he answered and told them, Elias verily cometh first, and restoreth all things; and how it is written of the Son of man, that he must suffer many things, and be set at nought. But I say unto you, That Elias is indeed come, and they have done unto him whatsoever they listed, as it is written of him.
(Hom. in Matt. 57) But what Christ answered to this, is seen by what follows, And he answered and told them, Elias verily cometh first, and restoreth all things; in which He shews that Elias will come before His second advent. For the Scriptures declare two advents of Christ, namely, one which has taken place, and another which is to come; but the Lord asserts that Elias is the forerunner of the second advent.