luke 1:17 And he shall go before him in the spirit and power of Elias, to turn the hearts of the fathers to the children, and the disobedient to the wisdom of the just; to make ready a people prepared for the Lord. - Free Bible Online

      17. before him--before "the Lord their God" (Lu 1:16). By comparing this with Mal 3:1 and Isa 40:3, it is plainly "Jehovah" in the flesh of Messiah [CALVIN and OLSHAUSEN] before whom John was to go as a herald to announce His approach, and a pioneer o prepare His way.
      in the spirit--after the model.
      and power of Elias--not his miraculous power, for John did no miracle" (Joh 10:41), but his power "turning the heart," or with like success in his ministry. Both fell on degenerate times; both witnessed fearlessly for God; neither appeared much save in the direct exercise of their ministry; both were at the head of schools of disciples; the success of both was similar.
      fathers to the children--taken literally, this denotes the restoration of parental fidelity [MEYER and others], the decay of which is the beginning of religious and social corruption--one prominent feature of the coming revival being put for the whole. But what follows, explanatory of this, rather suggests a figurative sense. If "the disobedient" be "the children," and to "the fathers" belongs "the wisdom of the just" [BENGEL], the meaning will be, "he shall bring back the ancient spirit of the nation into their degenerate children" [CALVIN, &c.]. So Elijah invoked "the God Abraham, Isaac, and Israel," when seeking to "turn their heart back again" (1Ki 18:36, 37).
      to make ready, &c.--more clearly, "to make ready for the Lord a prepared people," to have in readiness a people prepared to welcome Him. Such preparation requires, in every age and every soul, an operation corresponding to the Baptist's ministry.

JFB.