Mal 4:1
4:1 For, behold, the day cometh, that shall {a} burn as an oven;
    and all the proud, yea, and all that do wickedly, shall be
    stubble: and the day that cometh shall burn them up, saith
    the LORD of hosts, that it shall leave them neither root nor
    branch.

    (a) He prophesies of God's judgments against the wicked, who
        would not receive Christ, when God would send him for
        the restoration of his Church.

Mal 4:2
4:2 But unto you that fear my name shall the {b} Sun of
    righteousness arise with healing in his wings; and ye shall
    go {c} forth, and grow up as calves of the stall.

    (b) Meaning, Christ, who with his wings or beams of his
        grace would enlighten and comfort his Church; Eph 5:14.
        And he is called the "Sun of righteousness", because in
        himself he has all perfection, and also the justice of
        the Father dwells in him: by which he regenerates us
        to righteousness, cleanses us from the filth of this
        world, and reforms us to the image of God.
    (c) You will be set at liberty, and increase in the joy of
        the Spirit; 2Co 3:17.

Mal 4:4
4:4 {d} Remember ye the law of Moses my servant, which I
    commanded unto him in Horeb for all Israel, [with] the
    statutes and judgments.

    (d) Because the time had come that the Jews would be
        destitute of Prophets until the time of Christ, because
        they should with more fervent minds desire his coming,
        the Prophet exhorts them to exercise themselves
        diligently in studying the Law of Moses in the meantime,
        by which they might continue in the true religion, and
        also be armed against all temptations.

Mal 4:5
4:5 Behold, I will send you {e} Elijah the prophet before the
    coming of the great and {f} dreadful day of the LORD:

    (e) This Christ interprets of John the Baptist, who both for
        his zeal, and restoring or religion, is aptly compared
        to Elijah; Mt 11:13,14.
    (f) Which as it is true for the wicked, so does it waken the
        godly, and call them to repentance.

Mal 4:6
4:6 And he shall {g} turn the heart of the fathers to the
    children, and the heart of the children to their fathers,
    lest I come and {h} smite the earth with a curse.

    (g) He shows in what John's office would consist: in the
        turning of men to God, and uniting the father and
        children in one voice of faith: so that the father will
        turn to the religion of his son who is converted to
        Christ, and the son will embrace the faith of the true
        fathers, Abraham, Isaac, and Jacob.
    (h) The second point of his office was to give notice of God's
        judgment against those that would not receive Christ.