Elijah verily coming first restoreth all things: and how it is written — That is, And he told them how it is written — As if he had said, Elijah's coming is not inconsistent with my suffering. He is come: yet I shall suffer. The first part of the verse answers their question concerning Elijah; the second refutes their error concerning the Messiah's continuing for ever.
Related Commentaries of Mark 9:12
Mark 9:12
12 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.