John Lightfoot on John 1:25

[Why then baptizest thou?] The Jews likewise expected that the world should be renewed at the coming of the Messiah. "In those years wherein God will renew his world." Aruch, quoting these words, adds, "In those thousand years." So also the Gloss upon the place.

Amongst other things, they expected the purifying of the unclean. R. Solomon upon Ezekiel 36:26; "I will expiate you, and remove your uncleanness, by the sprinkling of the water of purification." Kimchi upon Zechariah 9:6; "The Rabbins of blessed memory have a tradition that Elias will purify the bastards and restore them to the congregation." You have the like in Kiddushin, Elias comes to distinguish the unclean and purify them, &c.

When therefore they saw the Baptist bring in such an unusual rite, by which he admitted the Israelites into a new rule of religion, they ask him by what authority he doth these things if he himself were not either the Messiah or Elias, or one of the prophets raised from the dead.

It is very well known that they expected the coming of Elias, and that, from the words of Malachi 4:5, not rightly understood. Which mistake the Greek version seems to patronise; I will send you Elias the Tishbite; which word the Tishbite, they add of themselves in favour of their own tradition; which indeed is too frequent a usage in that version to look so far asquint towards the Jewish traditions as to do injury to the sacred text.