Revelation 11

And I will give power to my two witnesses, and they will prophesy one thousand two hundred and sixty days, clothed in sackcloth.These are the two olive trees and the two lamp stands standing before the God of the earth. v.3-4

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The two witnesses. These two witnesses we read about in this chapter seem scary as they have power over nature and breath fire on their enemies. They prophesy for 1,260 days, or 3 1/2 years, till they are killed. Yet only for 3 1/2 days are their bodies lying dead till they are resurrected by God in the sight of many and then go up to heaven.
Who are these two witnesses? Many like to say one of these witnesses is Elijah, for prophesies say Elijah must come and restore all things yet this picture in Revelation doesn't fit Elijah's ministry to restore all things. Elijah's ministry will most likely be at the start of the kingdom of God when all will know the One and Only God. In Zechariah 3 & 4 we may have a clue as to who these two witnesses could be. In Zechariah there are two compared to olive branches and lamp stands referring to Zerubbabel as one and Joshua the high priest as the other. And further said of them, “These are the two anointed ones, who stand beside the Lord of the whole earth” (Zech. 4:14). So because of the context of the book of Zechariah we can better guess that these two witness are Zerubbabel the scribe and Joshua the high priest rather than Elijah, though we can't be complete sure.
Take heart that though these two witnesses are causing much turmoil and death, it's only turmoil and death to the enemies of the Lord. When they are resurrected back to life this is a sign that God is working again after this short time of the reign of the anitchrist in this tribulation period.