A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
mal 4:1GOD'S COMING JUDGMENT: TRIUMPH OF THE GODLY: RETURN TO THE LAW THE BEST PREPARATION FOR JEHOVAH'S COMING: ELIJAH'S PREPARATORY MISSION OF REFORMATION. (Mal 4:1-6)
the day cometh . . . burn-- (Mal 3:2; Pe2 3:7). Primarily is meant the judgment coming on Jerusalem; but as this will not exhaust the meaning, without supposing what is inadmissible in Scripture--exaggeration--the final and full accomplishment, of which the former was the earnest, is the day of general judgment. This principle of interpretation is not double, but successive fulfilment. The language is abrupt, "Behold, the day cometh! It burns like a furnace." The abruptness imparts terrible reality to the picture, as if it suddenly burst on the prophet's view.
all the proud--in opposition to the cavil above (Mal 3:15), "now we call the proud (haughty despisers of God) happy."
stubble-- (Oba 1:18; Mat 3:12). As Canaan, the inheritance of the Israelites, was prepared for their possession by purging out the heathen, so judgment on the apostates shall usher in the entrance of the saints upon the Lord's inheritance, of which Canaan is the type--not heaven, but earth to its utmost bounds (Psa 2:8) purged of all things that offend (Mat 13:41), which are to be "gathered out of His kingdom," the scene of the judgment being that also of the kingdom. The present dispensation is a spiritual kingdom, parenthetical between the Jews' literal kingdom and its antitype, the coming literal kingdom of the Lord Jesus.
neither root nor branch--proverbial for utter destruction (Amo 2:9).
mal 4:2The effect of the judgment on the righteous, as contrasted with its effect on the wicked (Mal 4:1). To the wicked it shall be as an oven that consumes the stubble (Mat 6:30); to the righteous it shall be the advent of the gladdening Sun, not of condemnation, but "of righteousness"; not destroying, but "healing" (Jer 23:6).
you that fear my name--The same as those in Mal 3:16, who confessed God amidst abounding blasphemy (Isa 66:5; Mat 10:32). The spiritual blessings brought by Him are summed up in the two, "righteousness" (Co1 1:30) and spiritual "healing" (Psa 103:3; Isa 57:19). Those who walk in the dark now may take comfort in the certainty that they shall walk hereafter in eternal light (Isa 50:10).
in his wings--implying the winged swiftness with which He shall appear (compare "suddenly," Mal 3:1) for the relief of His people. The beams of the Sun are His "wings." Compare "wings of the morning," Psa 139:9. The "Sun" gladdening the righteous is suggested by the previous "day" of terror consuming the wicked. Compare as to Christ, Sa2 23:4; Psa 84:11; Luk 1:78; Joh 1:9; Joh 8:12; Eph 5:14; and in His second coming, Pe2 1:19. The Church is the moon reflecting His light (Rev 12:1). The righteous shall by His righteousness "shine as the Sun in the kingdom of the Father" (Mat 13:43).
ye shall go forth--from the straits in which you were, as it were, held captive. An earnest of this was given in the escape of the Christians to Pella before the destruction of Jerusalem.
grow up--rather, "leap" as frisking calves [CALVIN]; literally, "spread," "take a wide range."
as calves of the stall--which when set free from the stall disport with joy (Act 8:8; Act 13:52; Act 20:24; Rom 14:17; Gal 5:22; Phi 1:4; Pe1 1:8). Especially the godly shall rejoice at their final deliverance at Christ's second coming (Isa 61:10).
mal 4:3Solving the difficulty (Mal 3:15) that the wicked often now prosper. Their prosperity and the adversity of the godly shall soon be reversed. Yea, the righteous shall be the army attending Christ in His final destruction of the ungodly (Sa2 22:43; Psa 49:14; Psa 47:3; Mic 7:10; Zac 10:5; Co1 6:2; Rev 2:26-27; Rev 19:14-15).
ashes--after having been burnt with the fire of judgment (Mal 4:1).
mal 4:4Remember . . . law--"The law and all the prophets" were to be in force until John (Mat 11:13), no prophet intervening after Malachi; therefore they are told, "Remember the law," for in the absence of living prophets, they were likely to forget it. The office of Christ's forerunner was to bring them back to the law, which they had too much forgotten, and so "to make ready a people prepared for the Lord" at His coming (Luk 1:17). God withheld prophets for a time that men might seek after Christ with the greater desire [CALVIN]. The history of human advancement is marked by periods of rest, and again progress. So in Revelation: it is given for a time; then during its suspension men live on the memories of the past. After Malachi there was a silence of four hundred years; then a harbinger of light in the wilderness, ushering in the brightest of all the lights that had been manifested, but short-lived; then eighteen centuries during which we have been guided by the light which shone in that last manifestation. The silence has been longer than before, and will be succeeded by a more glorious and awful revelation than ever. John the Baptist was to "restore" the defaced image of "the law," so that the original might be recognized when it appeared among men [HINDS]. Just as "Moses" and "Elias" are here connected with the Lord's coming, so at the transfiguration they converse with Him, implying that the law and prophets which had prepared His way were now fulfilled in Him.
statutes . . . judgments--ceremonial "statutes": "judgments" in civil questions at issue. "The law" refers to morals and religion.
mal 4:5I send you Elijah--as a means towards your "remembering the law" (Mal 4:4).
the prophet--emphatical; not "the Tishbite"; for it is in his official, not his personal capacity, that his coming is here predicted. In this sense, John the Baptist was an Elijah in spirit (Luk 1:16-17), but not the literal Elijah; whence when asked, "Art thou Elias?" (Joh 1:21), He answered, "I am not." "Art thou that prophet?" "No." This implies that John, though knowing from the angel's announcement to his father that he was referred to by Mal 4:5 (Luk 1:17), whence he wore the costume of Elijah, yet knew by inspiration that he did not exhaustively fulfil all that is included in this prophecy: that there is a further fulfilment (compare Note, see on Mal 3:1). As Moses in Mal 4:4 represents the law, so Elijah represents the prophets. The Jews always understood it of the literal Elijah. Their saying is, "Messiah must be anointed by Elijah." As there is another consummating advent of Messiah Himself, so also of His forerunner Elijah; perhaps in person, as at the transfiguration (Mat 17:3; compare Mat 17:11). He in his appearance at the transfiguration in that body on which death had never passed is the forerunner of the saints who shall be found alive at the Lord's second coming. Rev 11:3 may refer to the same witnesses as at the transfiguration, Moses and Elijah; Rev 11:6 identifies the latter (compare Kg1 17:1; Jam 5:17). Even after the transfiguration Jesus (Mat 17:11) speaks of Elijah's coming "to restore all things" as still future, though He adds that Elijah (in the person of John the Baptist) is come already in a sense (compare Act 3:21). However, the future forerunner of Messiah at His second coming may be a prophet or number of prophets clothed with Elijah's power, who, with zealous upholders of "the law" clothed in the spirit of "Moses," may be the forerunning witnesses alluded to here and in Rev 11:2-12. The words "before the . . . dreadful day of the Lord," show that John cannot be exclusively meant; for he came before the day of Christ's coming in grace, not before His coming in terror, of which last the destruction of Jerusalem was the earnest (Mal 4:1; Joe 2:31).
mal 4:6turn . . . heart of . . . fathers to . . . children, &c.--Explained by some, that John's preaching should restore harmony in families. But Luk 1:16-17 substitutes for "the heart of the children to the fathers," "the disobedient to the wisdom of the just," implying that the reconciliation to be effected was that between the unbelieving disobedient children and the believing ancestors, Jacob, Levi, "Moses," and "Elijah" (just mentioned) (compare Mal 1:2; Mal 2:4, Mal 2:6; Mal 3:3-4). The threat here is that, if this restoration were not effected, Messiah's coming would prove "a curse" to the "earth," not a blessing. It proved so to guilty Jerusalem and the "earth," that is, the land of Judea when it rejected Messiah at His first advent, though He brought blessings (Gen 12:3) to those who accepted Him (Joh 1:11-13). Many were delivered from the common destruction of the nation through John's preaching (Rom 9:29; Rom 11:5). It will prove so to the disobedient at His second advent, though He comes to be glorified in His saints (Th2 1:6-10).
curse--Hebrew, Cherem, "a ban"; the fearful term applied by the Jews to the extermination of the guilty Canaanites. Under this ban Judea has long lain. Similar is the awful curse on all of Gentile churches who love not the Lord Jesus now (Co1 16:22). For if God spare not the natural branches, the Jews, much less will He spare unbelieving professors of the Gentiles (Rom 11:20-21). It is deeply suggestive that the last utterance from heaven for four hundred years before Messiah was the awful word "curse." Messiah's first word on the mount was "Blessed" (Mat 5:3). The law speaks wrath; the Gospel, blessing. Judea is now under the "curse" because it rejects Messiah; when the spirit of Elijah, or a literal Elijah, shall bring the Jewish children back to the Hope of their "fathers," blessing shall be theirs, whereas the apostate "earth" shall be "smitten with the curse" previous to the coming restoration of all things (Zac 12:13-14).
May the writer of this Commentary and his readers have grace "to take heed to the sure word of prophecy as unto a light shining in a dark place, until the day dawn!" To the triune Jehovah be all glory ascribed for ever!