The two witnesses
Who the two witnesses are — Moses and Elijah, or the church's testimony — and what the days mean.
Revelation 11:1-13
1A reed like a rod was given to me. Someone said, “Rise, and measure God’s temple, and the altar, and those who worship in it.
2Leave out the court which is outside of the temple, and don’t measure it, for it has been given to the nations. They will tread the holy city under foot for forty-two months.
3I will give power to my two witnesses, and they will prophesy one thousand two hundred sixty days, clothed in sackcloth.”
4These are the two olive trees and the two lamp stands, standing before the Lord of the earth.
5If anyone desires to harm them, fire proceeds out of their mouth and devours their enemies. If anyone desires to harm them, he must be killed in this way.
6These have the power to shut up the sky, that it may not rain during the days of their prophecy. They have power over the waters, to turn them into blood, and to strike the earth with every plague, as often as they desire.
7When they have finished their testimony, the beast that comes up out of the abyss will make war with them, and overcome them, and kill them.
8Their dead bodies will be in the street of the great city, which spiritually is called Sodom and Egypt, where also their Lord was crucified.
9From among the peoples, tribes, languages, and nations, people will look at their dead bodies for three and a half days, and will not allow their dead bodies to be laid in a tomb.
10Those who dwell on the earth rejoice over them, and they will be glad. They will give gifts to one another, because these two prophets tormented those who dwell on the earth.
11After the three and a half days, the breath of life from God entered into them, and they stood on their feet. Great fear fell on those who saw them.
12I heard a loud voice from heaven saying to them, “Come up here!” They went up into heaven in the cloud, and their enemies saw them.
13In that day there was a great earthquake, and a tenth of the city fell. Seven thousand people were killed in the earthquake, and the rest were terrified, and gave glory to the God of heaven.
What each tradition says
Rabbinic / Midrashic
The Jewish Encyclopedia says that during this time there shall be two prophets, witnesses of the Lord, namely Moses and Elijah. They shall again manifest their power of restraining the heavens from giving rain, turning water into blood, and striking the land with plagues.
Jewish Encyclopedia (1905), article "Revelation (Book of)", The Jewish Encyclopedia (Funk & Wagnalls, 1901-1906) — "Moses and Elijah" (on xi. 3-7)
Patristic
Victorinus says many think Elisha or Moses is with Elijah, but both of these died, while Elijah’s death is not heard of. He notes that all the ancients believed Jeremiah was with Elijah.
Victorinus of Pettau, Commentary on the Apocalypse of the Blessed John — ANF vol. 7 (ed. Roberts & Donaldson) — From the eleventh chapter (on Rev. xi. 3-5)
Catholic
Haydock notes a very common interpretation holds the two witnesses to be Enoch and Elijah, who are to come before the end of the world. He observes several ancient Fathers taught this, and Dr. Wells calls it the consent of the primitive fathers and of unexceptionable authority.
George Leo Haydock, George Haydock's Catholic Bible Commentary (1859) — On Revelation 11:3 — the common interpretation (Enoch and Elias)
Catholic
Haydock reports that St. Cyprian interpreted the two witnesses as two sorts of martyrs for the Catholic faith: those who suffer death and those who suffer imprisonment, loss of goods, and the like. Others interpreted them as the testimonies concerning Christ and his Church, some in the Old Testament and some in the New.
George Leo Haydock, George Haydock's Catholic Bible Commentary (1859) — On Revelation 11:3 — the alternatives (St. Cyprian's two sorts of martyrs; the testimonies of both Testaments)
Orthodox
No sourced position found. Checked CCEL NPNF 2nd series (Cyril of Jerusalem's Catechetical Lectures npnf207 — including the lecture on Antichrist — Gregory of Nyssa npnf205; searched for "witnesses" and "Enoch" connections to Rev 11): no treatment of the two witnesses. archive.org offers only modern copyrighted translations of the Eastern Revelation commentators (Andrew of Caesarea 2012, Oecumenius 2006 — both lending-restricted). No public-domain Orthodox statement on Rev 11:1-13 found.
Reformed / Protestant
Matthew Henry notes some think the two witnesses are Enoch and Elias returning to earth, while others think they are the church of believing Jews and Gentiles. He says it rather seems they are God's eminent faithful ministers, who will continue to profess and preach the Christian religion even in the worst times.
Matthew Henry, An Exposition of the Old and New Testament (Matthew Henry's Commentary), vol. VI (Acts to Revelation) — On Revelation 11:3-6 ("The Two Witnesses")
Evangelical
John Wesley says the two witnesses seem to be two prophets—two select, eminent instruments. He notes some have supposed they are Moses and Elijah, though he says this is without foundation, while they resemble them in several respects.
John Wesley, John Wesley's Explanatory Notes on the New Testament — On Revelation 11:3 ("Will give to my two witnesses")