It says in the Old Testament, in
Malachi 4, that Elijah will return before the end. The Jews in OT times believed this prophecy to be literal and so did
St. John Chrysostom and other Catholic saints.
But fear not. “In those that perish” he will have his strength. For Elijah too will then come to give confidence to the faithful, and this Christ says; "Elijah comes, and shall restore all things."
Matthew 17:11 Therefore it is said, “In the spirit and power of Elijah.”
Luke 1:17 For he neither wrought signs nor wonders, as Elijah did. For “John,” it is said, “did no miracle, but all things which John spoke of this Man were true.” How then was it “in the spirit and power of Elijah”? That is, he will take upon him the same ministry. As the one was the forerunner of His first Coming, so will the other be of His second and glorious Coming, and for this he is reserved. Let us not therefore fear. He has calmed the minds of the hearers. He causes them no longer to think present things dreadful but worthy of thankfulness.
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St. John Chrysostom, Homily 4 on Second Thessalonians (circ. A.D. 391)
And here's what St. Bede said about it:
Some understand the two prophets to be Enoch and Elijah, and that they are to preach for three years and a-half, and confirm the hearts of the faithful against the perfidy of Antichrist, which is presently to follow; and that, after their death, his cruelty is to rage for the same period of time, and then, when the conflict is at length renewed by the saints, who in the protection of their hiding-places were supposed to be dead, is to be overcome. And these, because of their fellowship in one body, are said to rise as prophets themselves; and when the persecution is intensified at the sight of those who were already thought to be dead, many of those who were supposed to be worthy of the number seven, or ten, will fall. For Daniel says, “He will confirm the covenant with many for one week, and in the half of the week the oblation and sacrifice will cease, and the abomination of desolation shall be in the temple;” and the following, “and when the abomination which makes desolate shall be set up, there will be a thousand two hundred and ninety days,” which number is close upon the course of three years and a-half. Finally, Elijah of old destroyed his adversaries by fire, and was hidden for three years and a-half, and withheld the rain; and at length, when the false prophets were put to death, by means of the sacrifice which had been consumed, he turned Israel unto the Lord.
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St. Bede, The Explanation of the Apocalypse (circ. A.D. 710-716)
In Catholicism, we have Sacred Scripture AND divine Tradition to guide us in the interpretation of the word of God. It has been a constant tradition that Elijah will return, and it's been the belief of many Catholic saints that his return would be with Enoch.