Tower Of David (Citadel), Jerusalem by Wayne McLean (CC)
The scriptures tell of two witnesses who will prophesy in Jerusalem for two and half years just prior to the Second Coming of Jesus Christ.

The apostle John wrote about them in the book of Revelation:
And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth. These are the two olive trees, and the two candlesticks standing before the God of the earth.  (Revelation 11:3–4.)
Here is a brief summary of their ministry. Fire came out of the mouths of these prophets which destroyed their enemies. (That sounds like some kind of preaching. Wow.) They also shut up the heavens, causing a drought. After they were done bearing testimony in the city, power was given to the "beast" to kill them. While their bodies lay in the street, "people and kindreds and tongues and nations" rejoiced at their deaths and sent gifts to each other. (Could they see it on television or via the Internet?) After the three and a half days, the prophets rose from the dead and ascended into heaven, to the utter shock of their onlookers. Then there was a great earthquake and hail (see Revelation 11:5–12) which we've discussed in earlier posts.

The prophet Zechariah also prophesied of the "two olive trees":
Then answered I, and said unto him, What are these two olive trees upon the right side of the candlestick and upon the left side thereof? And I answered again, and said unto him, What be these two olive branches which through the two golden pipes empty the golden oil out of themselves? And he answered me and said, Knowest thou not what these be? And I said, No, my lord. Then said he, These are the two anointed ones, that stand by the Lord of the whole earth. (Zechariah 4:11–14; emphasis added.)
Isaiah also spoke of these two prophets:
These two things are come unto thee; who shall be sorry for thee? desolation, and destruction, and the famine, and the sword: by whom shall I comfort thee. Thy sons have fainted, they lie at the head of all the streets, as a wild bull in a net: they are full of the fury of the Lord, the rebuke of thy God. (Isaiah 51:l9, 20; emphasis added.)
Modern revelation provides the following explanation:
Q. What is to be understood by the two witnesses, in the eleventh chapter of Revelation?A. They are two prophets that are to be raised up to the Jewish nation in the last days, at the time of the restoration, and to prophesy to the Jews after they are gathered and have built the city of Jerusalem in the land of their fathers. (D&C 77:15; emphasis added.) 
The appearance of these prophets shows the pattern or law of witnesses:

In the mouth of two or three witnesses shall every word be established. (2 Corinthians 13:1.)

Two mighty prophets will prophesy in Jerusalem for several years before the coming of Christ. It appears that people across the globe will be aware of their ministry. They eventually will be killed but will in three days be resurrected and ascend into heaven. Not long after this will appear signs of the Second Coming of the Son of Man. What an incredible time this will be. 

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