Art thou Elijah? — He was not that Elijah (the Tishbite) of whom they spoke. Art thou the prophet — Of whom Moses speaks, Deuteronomy 18:15.
Related Commentaries of John 1:21
John 1:21
21 And they asked him, What then? Art thou Elias? And he saith, I am not. Art thou that prophet? And he answered, No.