The Two Witnesses [Revelation 11: 3-13]
"And I will grant authority to my two witnesses, and they will prophesy for twelve hundred and sixty days, clothed in sackcloth."  These are the two olive trees and the two candlesticks, standing before the Lord of the earth.  And if any man desireth to hurt them, fire proceedeth out of their mouth and devoureth their enemies; and if any man shall desire to hurt them, in this manner must he be killed.  These have the power to shut the heaven, that it rain not during the days of their prophecy: and they have power over the waters to turn them into blood, and to smite the earth with every plague, as often as they shall desire.  And when they shall have finished their testimony, the beast that cometh up out of the abyss shall make war with them, and overcome them, and kill them.  And their dead bodies lie in the street of the great city, which spiritually is called Sodom and Egypt, where also their Lord was crucified.  And from among the peoples and tribes and tongues and nations do men look upon their dead bodies three days and a half, and suffer not their dead bodies to be laid in a tomb.  And they that dwell on the earth rejoice over them, and make merry; and they shall send gifts one to another; because these two prophets tormented them that dwell on the earth.  And after the three days and a half the breath of life from God entered into them, and they stood upon their feet; and great fear fell upon them that beheld them.  And they heard a great voice from heaven saying unto them, Come up hither. And they went up into heaven in the cloud; and their enemies beheld them.  And in that hour there was a great earthquake, and the tenth part of the city fell; and there were killed in the earthquake seven thousand persons: and the rest were affrighted, and gave glory to the God of heaven. 
Note: The Greek in verse 3 simply says “And I shall give to my two witnesses.” What is given is not stated.
A summary of the above verses.. The witnesses can devour their enemies with fire from their mouths (5) they have the power to shut the heaven stopping the rain during the days of their prophecy, and the power to turn waters them into blood, and to smite the earth with every plague as often as they want (6) After their work is completed they will be killed (7), they will lie in the street for 3½ days (9), and then they will be brought to life and will be called up to heaven (11-12). In that hour there will be an earthquake with thousands of people killed (13).
Symbolic or Literal? Many have claimed that these two witnesses are merely symbolic… of a power or movement or even of the church. However this does not ring true for several reasons...
Besides the general tenor of the verses being that of a straight forward description of two exceptional individuals, the imagery of the olive trees and lampstands is borrowed from Zechariah 4, which refers to two actual individuals, Zerubbabel and Joshua.
The term “witness” in the New Testament is always used of persons. Under the law, two witnesses were required, and were enough, to establish any fact. Jesus even said that if the testimony of two men were sufficient to establish a fact, his own testimony and that of his Father ought to be esteemed ample evidence in the case of religious doctrine. [John 8:13-18]. Besides which, both Jesus and the early church sent out emissaries in pairs (See Mark 6:7, Acts 13:2, 15:39-40).
The two witnesses are said to call down all sorts of plagues at will (V. 6), This has can not be an ability of the church at large, but one bestowed on a few specially anointed prophets. Verses 7-9 say they will be killed at the hand of the beast and their bodies will lie in Jerusalem. However the entire church can not be destroyed by the beast, nor can their corpses lie in any single city. Note: Allowing the bodies of the two witnesses to lie unburied in the street was then, and now, considered an indignity. See Psalm 79:2-3.
In Revelation 11:12, the voice calls the witnesses into heaven, commanding them to “Come up here!”, which they immediately obey. The verb used is in the active voice, indicating that they participated in the action. The verb used in 1 Thessalonians 4:17 translated as “snatched up” is in the passive voice.. in other words those that are ‘snatched up’ do not have to do anything.
Therefore the account of the life of the two witnesses preaching in Jerusalem, followed by their death, resurrection and ascension is more than likely to be literal, as is the account of the earthquake that follows and the seven thousand individuals (round number?) who die in it. These events cause many to realize that God is neither asleep nor defeated.
Identity: The two individuals known as the "Two Witnesses" are only mentioned in eleven verses in the entire Bible, and yet they play a major role in the End Times. While their identity has again caused much speculation, the fact that God has not named them, probably means that He does not intend for us to identify them. See Who Are The Two Witnesses In The Book Of Revelation? (Below)
Mission: The two witnesses will prophesy for 1260 days, which is the same length of time (forty and two months) that the holy city will be trodden under foot, mentioned in verse 2. While the word “prophesy” does not necessarily mean that they will predict future events; but that they could in some manner publicly maintain the truth to the world.
However considering the nature of Hebrew prophecy which, more often than not, is a repeating pattern, it may be wise to give thought to the role of “two witnesses” in the Old Testament. Consider the following
Whoso killeth any person, the murderer shall be slain at the mouth of witnesses: but one witness shall not testify against any person that he die. [Numbers 35:30]
At the mouth of two witnesses, or three witnesses, shall he that is to die be put to death; at the mouth of one witness he shall not be put to death. [Deuteronomy 17:6]
One witness shall not rise up against a man for any iniquity, or for any sin, in any sin that he sinneth: at the mouth of two witnesses, or at the mouth of three witnesses, shall a matter be established. [Deuteronomy 19:15]
The verses are self explanatory. One witness was never enough to condemn an accused person… God’s law requiring at least two. It seems more than likely that in the end times, the Two Witnesses will fulfill a similar role, although it is uncertain whether they will point the finger at Satan and his minions, at an unbelieving world or both. Regardless, it seems that at their testimony a guilty verdict is rendered, bringing death and destruction… For starters as they are taken up into Heaven...
And in that hour there was a great earthquake, and the tenth part of the city fell; and there were killed in the earthquake seven thousand persons: and the rest were affrighted, and gave glory to the God of heaven. [Revelation 11:13]
Which brings us to the whole question of ...
Timing: When it is that the Two Witnesses make their appearance on the world stage is a very difficult question to answer. The account appears in Revelation 11:3-13. The verses immediately preceding the account (10:1 to 11:2) are definitely not part of the chronological sequence of the events of Revelation, but an interlude in the series of judgments. While the very next verse, following the account of the Two Witnesses, says
“The second woe is past; behold, the third woe is coming quickly.” [11:14]
Which makes their ministry seemingly to be placed between woes two and three… between the Sixth and Seventh Trumpets. The rejoicing that takes place when they are killed would then be a last hurrah before the end as the Seventh Trumpet/Seven Bowls would quickly follow. However it seems improbable that there is a 3 ½ year period (the length of time the Two Witnesses are said to prophesy) between the trumpets of the 6th and 7th angels.
On the other hand, when the Two Witnesses of Revelation are killed, at the end of their 1,260 days, the world rejoices and sends gifts to one another, which makes one wonder how bad a shape the world is in at this point, with the post offices (and gift shops?) open, which leads to the possibility that they will make their appearance during the tribulation of the church, when the world has not yet been significantly affected.
The beast is given power to “speak great things” for forty two months or 1,260 days [Revelation 13:5], which could mean that the mission of the Witnesses could run concurrently with the time of the Antichrist’s persecution of the church and the Gentiles trampling on the holy city for 42 months [Revelation 11:2-3]. When the Two Witnesses are taken up to heaven in a cloud there is a Great Earthquake on earth which destroys a tenth part of the city (Jerusalem) and kills seven thousand people. One certainly can not be dogmatic about it, but one has to wonder if this is the same earthquake that takes place at the opening of the sixth seal and the beginning of the tribulation of Seven Trumpets... which makes sense. At the mouth of two witnesses is the verdict rendered and “he that is to die be put to death”
Revelation 6:12 And I saw when he opened the sixth seal, and there was a great earthquake; and the sun became black as sackcloth of hair, and the whole moon became as blood;
And the angel taketh the censer; and he filled it with the fire of the altar, and cast it upon the earth: and there followed thunders, and voices, and lightnings, and an earthquake. And the seven angels that had the seven trumpets prepared themselves to sound. [Revelation 8:5-6]
See The Judgment of God.. The Seven Trumpets
Who Are The Two Witnesses In The Book Of Revelation?
“There are three primary viewpoints on the identity of the two witnesses in Revelation 11:3-12: (1) Moses and Elijah, (2) Enoch and Elijah, (3) two unknown believers whom God calls to be His witnesses in the end times.
(1) Moses and Elijah are seen as possibilities for the two witnesses due to the witnesses' power to turn water into blood (Revelation 11:6), which Moses is known for (Exodus chapter 7), and their power to destroy people with fire (Revelation 11:5), which Elijah is known for (2 Kings chapter 1). Also giving strength to this view is the fact that Moses and Elijah appeared with Jesus at the transfiguration (Matthew 17:3-4). Further, Jewish tradition expected Moses and Elijah to return in the future. Malachi 4:5 predicted the return of Elijah, and the Jews believed that God’s promise to raise up a prophet like Moses (Deuteronomy 18:15, 18) necessitated his return.
(2) Enoch and Elijah are seen as possibilities for the two witnesses because they are the two individuals whom God has taken to heaven apart from experiencing death (Genesis 5:23; 2 Kings 2:11). The fact that neither Enoch or Elijah have experienced death seems to qualify them to experience death and resurrection, as the two witnesses experience (Revelation 11:7-12). Proponents of this view claim that Hebrews 9:27 (all men die once) disqualifies Moses from being one of the two witnesses, as Moses has died once already (Deuteronomy 34:5). However, there are several others in the Bible who died twice—e.g., Lazarus, Dorcas, and the daughter of the synagogue ruler—so there is really no reason why Moses should be eliminated on this basis.
View (3) essentially argues that Revelation chapter 11 does not attach any famous identity to the two witnesses. If their identities were Moses and Elijah, or Enoch and Elijah, why would Scripture be silent about this? God is perfectly capable of taking two "ordinary" believers and enabling them to perform the same signs and wonders that Moses and Elijah did. There is nothing in Revelation 11 that requires us to assume a "famous" identity for the two witnesses.
Which view is correct? The possible weakness of (1) is that Moses has already died once, and therefore could not be one of the two witnesses, who die, which would make Moses a contradiction of Hebrews 9:27. Proponents of (1) will argue that all of the people who were miraculously resurrected in the Bible (e.g., Lazarus) later died again. Hebrews 9:27 is viewed, then, as a "general rule," not a universal principle. There are no clear weaknesses to view (2), as it solves the "die once" problem, and it makes sense that if God took two people to heaven without dying, Enoch and Elijah, it was to prepare them for a special purpose. There are also no clear weaknesses to view (3). All three views are valid and plausible interpretations that Christians can have. The identities of the two witnesses is an issue Christians should not be dogmatic about”.” [http://www.gotquestions.org/two-witnesses.html]