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.

Wesley's Notes

4:5 Behold I will send - Though the spirit of prophecy cease for four hundred years, yet at the expiring of those years, you shall have one sent, as great as Elijah. Elijah - Namely John the Baptist, who came in the spirit and power of Elijah, Luke 1:17, and therefore bears his name. Before - That is, immediately before; so he was born six months before Christ, and began his preaching a few years before Christ began to exercise his publick office. The great and dreadful day of the Lord - This literally refers to the times of vengeance upon the Jews, from the death of Christ to the final desolation of the city and temple, and by accommodation, to the end of the world.

Jamieson-Fausset-Brown Bible Commentary

5. I 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 (Lu 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 (Lu 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 [1197]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 (Mt 17:3; compare Mt 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. Re 11:3 may refer to the same witnesses as at the transfiguration, Moses and Elijah; Re 11:6 identifies the latter (compare 1Ki 17:1; Jas 5:17). Even after the transfiguration Jesus (Mt 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 Ac 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 Re 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).

Matthew Henry's Concise Commentary

4:4-6 Here is a solemn conclusion, not only of this prophecy, but of the Old Testament. Conscience bids us remember the law. Though we have not prophets, yet, as long as we have Bibles, we may keep up our communion with God. Let others boast in their proud reasoning, and call it enlightening, but let us keep near to that sacred word, through which this Sun of Righteousness shines upon the souls of his people. They must keep up a believing expectation of the gospel of Christ, and must look for the beginning of it. John the Baptist preached repentance and reformation, as Elijah had done. The turning of souls to God and their duty, is the best preparation of them for the great and dreadful day of the Lord. John shall preach a doctrine that shall reach men's hearts, and work a change in them. Thus he shall prepare the way for the kingdom of heaven. The Jewish nation, by wickedness, laid themselves open to the curse. God was ready to bring ruin upon them; but he will once more try whether they will repent and return; therefore he sent John the Baptist to preach repentance to them. Let the believer wait with patience for his release, and cheerfully expect the great day, when Christ shall come the second time to complete our salvation. But those must expect to be smitten with a sword, with a curse, who turn not to Him that smites them with a rod. None can expect to escape the curse of God's broken law, nor to enjoy the happiness of his chosen and redeemed people, unless their hearts are turned from sin and the world, to Christ and holiness. The grace of our Lord Jesus Christ be with us all. Amen.