11 I was given a reed like a measuring rod and was told, "Go and measure the temple of God and the altar, and count the worshipers there.

Go and measure the temple of God and the altar. This was the directive God gave Zerubbabel (Zech 4:10). You only do measurements when you are planning on expanding. He is encouraging John that the church must expand.

   2 But exclude the outer court; do not measure it, because it has been given to the Gentiles. They will trample on the holy city for 42 months.

42 months. This is half of seven years. This time period is meant to take us back to Daniel 9 where the anti-Christ will break the covenant with God’s people.

3 And I will give power to my two witnesses, and they will prophesy for 1,260 days, clothed in sackcloth."

4 These are the two olive trees and the two lampstands that stand before the Lord of the earth.

two olive trees and the two lampstands. Zerubbabel saw a similar vision except he only saw two olive trees that were giving oil to lampstands. In this vision John sees two lampstands as well. In chapter one we know the lampstands to be the church.

5 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.

fire comes from their mouths. A description of God’s Word. See 9:17.

6 These men have power to shut up the sky 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.

A clear description of Elijah and Moses. Do not take this literally, but ask what does Moses and Elijah represent? Moses is the giver of the “Law” and Elijah is a “Prophet.” This is a description of the “Law and the Prophets”—a very common term for scripture (see Matt 7:12; 11:13; 22:40 and Lk 16:16). The two witnesses could also refer to the church as the reliable witnesses of the gospel.

7 Now when they have finished their testimony, the beast that comes up from the Abyss will attack them, and overpower and kill them.

attack them. Scriptures are always attacked by skeptics.

8 Their bodies will lie in the street of the great city, which is figuratively called Sodom and Egypt, where also their Lord was crucified.

where also their Lord was crucified. Jesus was literally crucified near Jerusalem, but John is using two sinful places to describe how awful the world can be toward the word of God.  

9 For three and a half days men from every people, tribe, language and nation will gaze on their bodies and refuse them burial.

10 The inhabitants of the earth will gloat over them and will celebrate by sending each other gifts, because these two prophets had tormented those who live on the earth.

11 But after the three and a half days a breath of life from God entered them, and they stood on their feet, and terror struck those who saw them.

after the three and a half days a breath of life from God entered them. Same length of time when Jesus was resurrected. John is saying to the world, “You may try to destroy the word of God, but you can never succeed.”

12 Then they heard a loud voice from heaven saying to them, "Come up here." And they went up to heaven in a cloud, while their enemies looked on.

13 At that very hour there was a severe earthquake and a tenth of the city collapsed. Seven thousand people were killed in the earthquake, and the survivors were terrified and gave glory to the God of heaven.

Seven thousand people. Seven is the number of completion.

14 The second woe has passed; the third woe is coming soon.

The second woe has passed. The sounding of the sixth trumpet—200 million troops, John eating the scroll, and the two witnesses are all related. This second woe is about evangelism.

15 The seventh angel sounded his trumpet, and there were loud voices in heaven, which said:

"The kingdom of the world has become the kingdom of our Lord and of his Christ,

and he will reign for ever and ever."

seventh angel sounded his trumpet. This is the final trumpet and it signifies that all has finally been completed. We look forward to that time.

16 And the twenty-four elders, who were seated on their thrones before God, fell on their faces and worshiped God,

17 saying:

"We give thanks to you, Lord God Almighty,

the One who is and who was,

because you have taken your great power

and have begun to reign.

18 The nations were angry;

and your wrath has come.

The time has come for judging the dead,

and for rewarding your servants the prophets

and your saints and those who reverence your name,

both small and great —

and for destroying those who destroy the earth."

19 Then God's temple in heaven was opened, and within his temple was seen the ark of his covenant. And there came flashes of lightning, rumblings, peals of thunder, an earthquake and a great hailstorm.

ark of his covenant. The vision of the seven trumpets ends in the same way Joshua’s triumph over Jericho ends, with the priests carrying the ark of the covenant.