From Revelation 11 (KJ21):
3 And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth.”
4 These are the two olive trees and the two candlesticks, standing before the God of the earth.
Who are these two witnesses?
Who are the two witnesses in Revelation?
This response to the above question will be from a Catholic point of view.
According to the majority of Catholic writers, the Two Witnesses of Chapter 11 of the Apocalypse will be the Prophets Enoch and Elijah. They are also believed to be the "Two Witnesses" by many others Christian denominations likewise.
To start with let us look at what Wikipedia has to say on this subject:
In the Book of Revelation, the two witnesses are two of God's prophets who are seen in a vision by John of Patmos, who appear during the Second woe recorded in Revelation 11:1-14. They have been variously identified by theologians as two individuals, as two groups of people, or as two concepts. Dispensationalist Christians believe that the events described in the Book of Revelation will occur before and during the Second Coming of Christ.
Biblical narrative
John is told that the court of God's temple would be trampled on by the nations for 42 months. During that period for 1,260 days (or 42 months, or 3½ years), two witnesses would be granted authority to prophesy. They are described as two olive trees and two lampstands who stand before the Lord of the earth. Both are able to devour their enemies with fire that flows out of their mouths. Also, they have power over the sky and waters and are able to strike the earth with plague.
After their testimony, the Beast overcomes the two witnesses and kills them. For three and a half days, the people of the earth celebrate the two witnesses' death (who have tormented them for three and a half years) and will not permit the witnesses a proper burial. After this time, God resurrects the two witnesses; their resurrection strikes fear on everyone witnessing their revival, and the two witnesses then ascend to heaven. In the next hour, a great earthquake occurs and kills 7000 men, destroying a tenth of the city.
Identity
Early Christian writers such as Tertullian, Irenaeus, and Hippolytus of Rome, have concluded that the two witnesses would be Enoch and Elijah, prophets who did not die because God "took" them according to other Biblical passages.
Others have proposed Moses as one of the witnesses, for his ability to turn water into blood and the power to plague the earth.
Of all the Prophet mentioned in the Old Testament, only the prophets Enoch and Elijah has not died.
"By faith Enoch was translated that he should not see death; and was not found, because God had translated him: for before his translation he had this testimony, that he pleased God." This suggests he did not experience the mortal death ascribed to Adam's other descendants which is consistent with Genesis 5:24(KJV), which says, "And Enoch walked with God: and he [was] not; for God took him."
And as for Elijah:
According to 2 Kings 2:3–9, Elisha (Eliseus) and "the sons of the prophets" knew beforehand that Elijah would one day be assumed into heaven. Elisha asked Elijah to "let a double portion" of Elijah's "spirit" be upon him. Elijah agreed, with the condition that Elisha would see him be "taken".
Elijah, in company with Elisha, approaches the Jordan. He rolls up his mantle and strikes the water.[36] The water immediately divides and Elijah and Elisha cross on dry land. Suddenly, a chariot of fire and horses of fire appear and Elijah is lifted up in a whirlwind. As Elijah is lifted up, his mantle falls to the ground and Elisha picks it up.
Although most Catholic and other Christian writers favor the opinion that the two witnesses will be Enoch and Elijah, some claim that they may be Moses, John the Baptist or one of the other Jewish prophets.
Many have sought to identify the two witnesses. Some say Moses and Elijah and some Preterits state that these two witnesses represent all the prophets and John the Baptist (e.g. Chilton). However, the Church Fathers identified them as “Henoch and Elias” or “Enoch and Elijah” (Augustine). The reason for this is that Enoch and Elijah are the two Old Testament saints who were assumed into Heaven prior to death. Neither of them died. Their future death will be a martyrdom under the hand of the eschatological Antichrist.
This fact is confirmed by Saint Thomas Aquinas in his Summa Theologiae:
“Reply to Objection 2. Elias was taken up into the atmospheric heaven, but not in to the empyrean heaven, which is the abode of the saints: and likewise Enoch was translated into the earthly paradise, where he is believed to live with Elias until the coming of Antichrist. (Summa Theologiae III, q. 49, a. 5)"
Saint Thomas teaches that these two men are not in empyrean heaven (i.e. the supernatural realm) but are in the atmospheric heaven (outer space?). Whatever the situation, they are waiting for their encounter with the Antichrist. At least that’s what Saint Augustine and Saint Thomas Aquinas teach–and it’s difficult to argue with them. - Enoch and Elijah as the Two Witnesses of the Book of Revelation
The Catholic Church goes one step further in regard to the Prophet Elijah. The Carmelite Order celebrates the Feast of St. Elijah with red vestment in view of his future martyrdom.
Most of the early fathers of the Church identify Elias as one of the "two witnesses" in Chapter 11 of the Apocalypse, who do battle with the Antichrist. The two witnesses are martyred by the son of perdition, but their resurrection and ascension into Heaven ushers in the final defeat of "the beast." (see Apocalypse 11) The exact manner in which such cryptic prophecies will be fulfilled remains to be seen. It is interesting, however, that Carmelites have always used red vestments on July 20 in honor of the martyrdom of Elias that is to come. - July 20, Feast of St. Elias the Prophet, Leader and the Father of the Carmelites
