If one is not in Jerusalem at the time, one will not know. As it was, that event is over and the witnesses were there not to confirm the prophesy but to give something to the people living there. They were his representatives in the most difficult of all times. They did their part.
How can people from every nation, tribe, people and language view the bodies of the two witnesses lying in the streets of Jerusalem? You ever hear of webcams and the news media?
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"When the two witnesses have finished their testimony, the beast that comes up from the Abyss will wage war with them, and will overpower and kill them. Their bodies will lie in the street of the great city—figuratively called Sodom and Egypt—where their Lord was also crucified.
For three and a half days all peoples and tribes and languages and nations will view their bodies and will not permit them to be laid in a tomb. And those who dwell on the earth will gloat over them, and will celebrate and send one another gifts, because these two prophets had tormented them"
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These two witnesses being killed by the beast is a future event. The beast is released at the sounding of the 5th trumpet. He's that angel of the Abyss called Abaddon/Apollyon, meaning destroyer.
The two witnesses will do just exactly as scripture states, they will prophesy for 1260 days (3 1/2 years). The scripture does not say that they are there to give something to the people who live there, but to prophesy to them regarding God and the eternal gospel.
And it's not "They were his representatives" but "will be his representatives" future tense. These two witnesses will be able to bring any plague they like upon the earth, as often as they want. The people of the earth will hate them because of their plagues and will celebrate by sending gifts to each other after the beast who comes up out of the Abyss kills them. Three and a half days later, the two witnesses will stand up (resurrect) and all the inhabitants of the earth who will have been gloating over them, will be filled with fear when they stand back up and ascend into heaven before their very eyes.