In an article by a Catholic apologist (I believe it is David Palm, but it is anonymous), we read the following, in response to another Catholic, Robert Sungenis, about a post-New Testament coming of Elijah (something Sungenis rejects). As Latter-day Saints believe that Mal 4:5-6 was not fulfilled, at least completely, by John the Baptist, but by a then-future coming of Elijah, this will be of interest to LDS, not just Catholics:
Question: What is the Real Foundation of the Belief in a Future Coming of Elijah?
Answer: The Sacred Scriptures.
The main verse that illuminates this belief, which Bob criticizes, is Mal 4:5-6:
Behold, I will send you Elias the prophet, before the coming of the great and dreadful day of the Lord. And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers: lest I come, and strike the earth with anathema.
Although it’s clear that these verses have at least a partial fulfillment in the coming of St. John the Baptist (see Matt 11:14), there are several details even in the prediction from Malachi—most notably the mention of “the great and dreadful day of the Lord”—which would suggest that there is another fulfillment in connection with the Second Coming of Christ.
This is strengthened by another passage of sacred Scripture—rejected by Protestants, but known by Catholics to be inspired Scripture—namely, Sirach 48:1-10, which reads:
And Elias the prophet stood up, as a fire, and his word burnt like a torch. He brought a famine upon them, and they that provoked him in their envy, were reduced to a small number, for they could not endure the commandments of the Lord. By the word of the Lord he shut up the heaven, and he brought down fire from heaven thrice. Thus was Elias magnified in his wondrous works. And who can glory like to thee? Who raisedst up a dead man from below, from the lot of death, by the word of the Lord God. Who broughtest down kings to destruction, and brokest easily their power in pieces, and the glorious from their bed. Who heardest judgment in Sina, and in Horeb the judgments of vengeance. Who anointedst kings to penance, and madest prophets successors after thee. Who wast taken up in a whirlwind of fire, in a chariot of fiery horses. Who art registered in the judgments of times to appease the wrath of the Lord, to reconcile the heart of the father to the son, and to restore the tribes of Jacob (my emphasis).
This is an important application of the prophecy from the Prophet Malachi, from another passage of sacred Scripture. Notice that from start to finish it is speaking explicitly of the Old Testament prophet Elijah. Notice too that the last verse cited, v. 10, is clearly an application of the prophecy of Malachi 4:5-6 to that same Elijah. The presentation of Elijah’s deeds is chronological and he is said to appease the Lord’s wrath, reconcile father and son, and “restore the tribes of Jacob” after he was “taken up in a whirlwind of fire” into heaven—thus it cannot be part of the prophet Elijah’s first earthly ministry. And importantly, there is no indication whatsoever that when we come to verse 10 we are suddenly to think, not of the original prophet Elijah, but now exclusively of St. John the Baptist. There is no hint that there is any change of subject.
Did St. John the Baptist fulfill the prophecy of Mal 4:5-6? Of course, he did. He came, as the angel said to our Lady, “in the spirit and power of Elijah” (Luke 1:17). But was that a complete fulfillment of Mal 4:5-6? Certainly Sirach 48:10 would indicate that it was not. And now here's what our Lord says about Elijah/John the Baptist:
And the disciples asked him, "Then why do the scribes say that first Eli'jah must come?" He replied, "Eli'jah does come, and he is to restore all things; but I tell you that Eli'jah has already come, and they did not know him, but did to him whatever they pleased. So also the Son of man will suffer at their hands." Then the disciples understood that he was speaking to them of John the Baptist (Matt 17:10-13; my emphasis).
That's the Revised Standard Version (RSV) translation. Here's the Douay-Rheims (DR):
And his disciples asked him, saying: Why then do the scribes say that Elias must come first? But he answering, said to them: Elias indeed shall come, and restore all things. But I say to you, that Elias is already come, and they knew him not, But have done unto him whatsoever they had a mind. So also the Son of man shall suffer from them. Then the disciples understood, that he had spoken to them of John the Baptist (my emphasis).
Notice first of all that these words were said after St. John the Baptist had been executed by Herod. He had already been put to death by Herod.
A couple of other interesting things really stand out in this passage (especially vv. 10-11). First, it's set up in Greek using a μὲν - δὲ construction, which means "on the one hand .... on the other hand". This is not brought out very well in the English translations, but it's concrete in Greek.
So on the one hand....μὲν....what? Our Lord says that "Elijah does come" or (in the DR) "Elijah indeed shall come". The Greek verb is ἔρχεται which is the present middle/passive indicative of the verb ἔρχomαι which means "to come". So this is literally translated "he is coming". Even after St. John the Baptist is dead, our Lord states that "Elijah is coming", something that seems to suggest a future fulfillment. In addition, in verse 10 our Lord stated, "he [Elijah] will restore all things". The verb is ἀποκαταστήσει, a straightforward future active indicative. Again, after St. John the Baptist is dead, our Lord states that Elijah will—in the future—restore all things. This is clearly not something that St. John did during his lifetime; it is something that belongs yet to the future.
And "on the other hand".....δὲ....what? In verse 11 the verb is ἦλθεν, the aorist active indicative of the same verb ἔρχomαι, rightly translated as a past tense, "he has come". This, of course, is looking back to St. John the Baptist. And "they knew him not" again clearly looking back in the past to St. John.
The Fathers of the Church saw here a both/and rather than an either/or. There is certainly a fulfillment of Mal 4:5-6 by St. John the Baptist, so that he can indeed be spoken of as "Elijah". And yet to the Fathers there remained a future, more literal fulfillment of the prophecy by Elijah himself. Indeed, even St. John the Baptist, when asked whether he was actually Elijah, said “I am not” (John 1:21).
This juxtaposition of the already and the not yet is summarized well by renowned biblical scholar, Fr. Leo Haydock:
The prophet Elias will come again in person before [our Lord’s] second coming to judgment, and will re-establish all things, by the conversion of the Jews to the Christian faith, according to the common opinion. But John the Baptist who was Elias in spirit, is already come. . . . The Baptist was the precursor of Christ at his first coming, and was styled by our Lord Elias, because he performed the office of Elias; and he shall go before Him in the spirit and power of Elias. (Luke i. 17.) --- But this prophet in person will be the precursor of the second coming of Christ. . . . Jesus Christ here confirms the literal sense of the prophecy; (Malachias iv. 5,) but in the next verse, he shews a prior, though less perfect accomplishment of the same in the person of John the Baptist, who was raised by God to prepare the ways of the Lord.
Cf. also renowned biblical scholar, Fr. Cornelius de Lapide:
Falsely do the Calvinists refer all these things to the first Advent of Christ, and explain both mentions of Elias—viz., in verses 11 and 12—to mean John the Baptist. For they think that Elias, whom Malachi predicted shall come as the precursor of Christ (iv. 5), is John the Baptist, and that there is no other who shall come with Enoch before Christ’s second Advent. (http://www.catholicapologetics.info/scripture/newtestament/17matth.htm)
This idea that there are comings of Elijah in conjunction with both the first and second coming of our Lord is laid out by numerous Fathers of the Church. St. Justin Martyr, writing c. A.D. 160, had this to say:
Justin: Does not Scripture, in the book of Zechariah, Malachi 4:5 say that Elijah shall come before the great and terrible day of the Lord?
Trypho: Certainly.
Justin: If therefore Scripture compels you to admit that two advents of Christ were predicted to take place—one in which He would appear suffering, and dishonoured, and without comeliness; but the other in which He would come glorious and Judge of all, as has been made manifest in many of the fore-cited passages—shall we not suppose that the word of God has proclaimed that Elijah shall be the precursor of the great and terrible day, that is, of His second advent?
Trypho: Certainly.
Justin: And, accordingly, our Lord in His teaching proclaimed that this very thing would take place, saying that Elijah would also come. And we know that this shall take place when our Lord Jesus Christ shall come in glory from heaven; whose first manifestation the Spirit of God who was in Elijah preceded as herald in [the person of] John, a prophet among your nation; after whom no other prophet appeared among you.
Already in the second century the Fathers saw that Scripture supported the idea of an appearance of Elijah to accompany both the first and second comings of Christ. Another early Father, Tertullian, lays this out even more clearly:
But Elias is to come again, not after quitting life (in the way of dying), but after his translation (or removal without dying); not for the purpose of being restored to the body, from which he had not departed, but for the purpose of revisiting the world from which he was translated; not by way of resuming a life which he had laid aside, but of fulfilling prophecy—really and truly the same man, both in respect of his name and designation, as well as of his unchanged humanity. How, therefore could John be Elias? You have your answer in the angel's announcement: "And he shall go before the people," says he, "in the spirit and power of Elias"— not (observe) in his soul and his body.”
Even Sungenis has to admit that Tertullian “was one of the more vocal proponents of both Chiliasm and the Enoch/Elijah theory” and “he seems to be reiterating an idea that came prior to him” (CASB3, p. 443).
For more, see: