Revelation 11:5-6

 "And behold, I am coming quickly. 

Blessed is he who heeds the words of the prophecy of this book."     

Revelation 22:7  NASB

If anyone tries to harm them, fire comes from their mouths and devours their enemies. This is how anyone who wants to harm them must die. They have power to shut up the heavens so that it will not rain during the time they are prophesying; and they have power to turn the waters into blood and to strike the earth with every kind of plague as often as they want. 

If anyone tries to harm them, fire comes from their mouths and devours their enemies 
2 Samuel 22:9  "Smoke rose from his (God's) nostrils; consuming fire came from his mouth, burning coals blazed out of it."
2 Kings 1:10  Elijah answered the captain, "If I am a man of God, may fire come down from heaven and consume you and your fifty men!" Then fire fell from heaven and consumed the captain and his men.
Jeremiah 5:14  Therefore this is what the LORD God Almighty says: "Because the people have spoken these words, I will make my words in your mouth a fire and these people the wood it consumes."
Revelation 9:17-18  The horses and riders I saw in my vision looked like this: Their breastplates were fiery red, dark blue, and yellow as sulfur. The heads of the horses resembled heads of lions, and out of their mouths came fire, smoke and sulfur. A third of mankind was killed by the three plagues of fire, smoke and sulfur that came out of their mouths. 

This is how anyone who wants to harm them must die 
Numbers 16:29  "If these men die a natural death and suffer the fate of all mankind, then the LORD has not sent me."
Numbers 16:35  And fire came out from the LORD and consumed the 250 men who were offering the incense.

They have the power to shut up the heavens 
Luke 4:25  "I assure you that there were many widows in Israel in Elijah's time, when the sky was shut for three and a half years and there was a severe famine throughout the land."

so that it will not rain during the time they are prophesying 
Revelation 11:3  "And I will appoint my two witnesses, and they will prophesy for 1,260 days (three and a half years), clothed in sackcloth."

and they have the power to turn the waters into blood 
Exodus 7:17  The LORD said to Moses, "Tell Aaron, 'Take your staff and stretch out your hand over the waters of Egypt--over the streams and canals, over the ponds and all the reservoirs--and they will turn to blood.' Blood will be everywhere in Egypt, even in vessels of wood and stone."
Revelation 8:8-9  The second angel sounded his trumpet, and something like a huge mountain, all ablaze was thrown into the sea. A third of the sea turned to blood, and a third of the living creatures in the sea died, and a third of the ships were destroyed.

(parentheses are mine)

Scriptures taken from the Holy Bible, New International Version® NIV®, Copyright© 1973, 1978, 1984, 2011 by Biblica, Inc.® Used by permission. All rights reserved worldwide. 
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