Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD: Behold, I will send you Elijah - as a means toward your "remembering the law" (Malachi 4:4).
The prophet - emphatic: 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 (Luke 1:16-17), but not the literal Elijah; whence, when asked, "Art thou Elias?" (John 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 Malachi 4:5 (Luke 1:17), whence he wore the costume of Elijah, yet knew by inspiration that he did not exhaustively fulfill all that is included in this prophecy; that there is a further fulfillment (cf. note, Malachi 3:1). As Moses in Malachi 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 (Matthew 17:3: cf. Matthew 17:11, "Elias truly SHALL first come, and restore all things:" cf. Acts 3:21, "the times of restitution of all things," which proves that the time of the second coming is referred to).
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. Revelation 11:3 may refer to the same witnesses as at the transfiguration, Moses and Elijah; Revelation 11:6 identifies the latter (cf. 1 Kings 17:1; James 5:17). Even after the transfiguration, Jesus (Matthew 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. However, the future forerunner of Messiah at His second coming may be a prophet, or a number of prophets, clothed with Elijah's power, who, with zealous upholders of the "law," cothed in the spirit of "Moses," may be the forerunning witnesses alluded to here and in Revelation 11:2-12.
Before the coming of the great and dreadful day of the Lord. The words, "before the ... dreadful day of the Lord," show that John cannot be exclusively meant; because 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 (Malachi 4:1; Joel 2:31).