Tenses in the book of Revelation

Revelation 1:4 John, to the seven assemblies that are in Asia: Grace to you and peace from God, who is and who was and who is to come; and from the seven Spirits who are before his throne;
 
1:7 Behold, he is coming with the clouds, and every eye will see him, including those who pierced him. All the tribes of the earth will mourn over him. Even so, Amen.
 
3:11a I am coming quickly!
 
3:15 “I know your works, that you are neither cold nor hot. I wish you were cold or hot. 16  So, because you are lukewarm, and neither hot nor cold, I will vomit you out of my mouth.
 
4:1 After these things I looked and saw a door opened in heaven, and the first voice that I heard, like a trumpet speaking with me, was one saying, “Come up here, and I will show you the things which must happen after this.”
 
4:8 The four living creatures, each one of them having six wings, are full of eyes around and within. They have no rest day and night, saying, “Holy, holy, holy is the Lord God, the Almighty, who was and who is and who is to come!”
9 When the living creatures give glory, honor, and thanks to him who sits on the throne, to him who lives forever and ever, 10a the twenty-four elders fall down before him who sits on the throne, and worship him who lives forever and ever...

5:3 No one in heaven above, or on the earth, or under the earth, was able to open the book or to look in it. 4 Then I wept much, because no one was found worthy to open the book or to look in it. 5 One of the elders said to me, “Don’t weep. Behold, the Lion who is of the tribe of Judah, the Root of David, has overcome: he who opens the book and its seven seals.” 6a I saw in the middle of the throne and of the four living creatures, and in the middle of the elders, a Lamb standing, as though it had been slain ...

6:1 I saw that the Lamb opened one of the seven seals, and I heard one of the four living creatures saying, as with a voice of thunder, “Come and see!”
 
7:13 One of the elders answered, saying to me, “These who are arrayed in the white robes, who are they, and where did they come from?”
14 I told him, “My lord, you know.”
He said to me, “These are those who came out of the great tribulation. They washed their robes, and made them white in the Lamb’s blood. 15a Therefore they are before the throne of God, they serve him day and night in his temple. 
 
11:3 I will give power to my two witnesses, and they will prophesy one thousand two hundred sixty days, clothed in sackcloth.” 4 These are the two olive trees and the two lamp stands, standing before the Lord of the earth. 5 If anyone desires to harm them, fire proceeds out of their mouth and devours their enemies. If anyone desires to harm them, he must be killed in this way. 6 These have the power to shut up the sky, that it may not rain during the days of their prophecy. They have power over the waters, to turn them into blood, and to strike the earth with every plague, as often as they desire. 7 When they have finished their testimony, the beast that comes up out of the abyss will make war with them, and overcome them, and kill them. 8 Their dead bodies will be in the street of the great city, which spiritually is called Sodom and Egypt, where also their Lord was crucified. 9 From among the peoples, tribes, languages, and nations, people will look at their dead bodies for three and a half days, and will not allow their dead bodies to be laid in a tomb. 10 Those who dwell on the earth rejoice over them, and they will be glad. They will give gifts to one another, because these two prophets tormented those who dwell on the earth. 11 After the three and a half days, the breath of life from God entered into them, and they stood on their feet. Great fear fell on those who saw them.
 
14:17 Another angel came out of the temple which is in heaven. He also had a sharp sickle. 18 Another angel came out from the altar, he who has power over fire, and he called with a great voice to him who had the sharp sickle, saying, “Send your sharp sickle, and gather the clusters of the vine of the earth, for the earth’s grapes are fully ripe!” 19 The angel thrust his sickle into the earth, and gathered the vintage of the earth, and threw it into the great wine press of the wrath of God. 20 The wine press was trodden outside of the city, and blood came out of the wine press, even to the bridles of the horses, as far as one thousand six hundred stadia.

Revelation 17:8 The beast that you saw was, and is not; and is about to come up out of the abyss and to go into destruction. Those who dwell on the earth and whose names have not been written in the book of life from the foundation of the world will marvel when they see that the beast was, and is not, and shall be present.
 
20:7 And after the thousand years, Satan will be released from his prison, 8 and he will come out to deceive the nations which are in the four corners of the earth, Gog and Magog, to gather them together to the war; the number of whom is as the sand of the sea. 9 They went up over the width of the earth, and surrounded the camp of the saints, and the beloved city. Fire came down out of heaven from God and devoured them. 10 The devil who deceived them was thrown into the lake of fire and sulfur, where the beast and the false prophet are also. They will be tormented day and night forever and ever. 

21:1 I saw a new heaven and a new earth: for the first heaven and the first earth have passed away, and the sea is no more. 2 I saw the holy city, New Jerusalem, coming down out of heaven from God, prepared like a bride adorned for her husband.

21:5 He who sits on the throne said, “Behold, I am making all things new.” He said, “Write, for these words of God are faithful and true.” 6 He said to me, “I have become the Alpha and the Omega, the Beginning and the End. I will give freely to him who is thirsty from the spring of the water of life. 7  He who overcomes, I will give him these things. I will be his God, and he will be my son.
 
22:12 “Behold, I come quickly. My reward is with me, to repay to each man according to his work. 13 I am the Alpha and the Omega, the First and the Last, the Beginning and the End.

All Bible quotations above, from Revelation, are from the World English Bible, public domain. I am grateful. Emphasis added. These quotations are among many which have some indication of tense -- whether things have already happened, or will happen in the future. There are many other such passages in Revelation. I make no claim to be an expert on Revelation, which is, to say the least, a difficult book to understand, and have seldom posted on that book. (But see here.)

One thing that Revelation indicates is that Christ is eternal, as in 1:4, 21:6, and 22:12-13. He was, and is, and will be. Another truth is that He is returning in triumph. See the first three quotations above, and the last one, and many others throughout the book. Whatever the beast of Revelation 17 represents, is almost eternal -- was, is not, and is again, long enough to be destroyed.

Chapters 2 and 3 are, apparently, messages to seven churches. (They are probably also meant as messages to subsequent readers, including us.) Verses 3:15-16 are an example that seems to say that Christ is going to judge these churches, in the future, perhaps in the near future.

4:1 introduces us to the rest of the book, which is apocalyptic and prophetic, and, based on that verse, is about things which are to come.

4:8-10 reiterate that the triumphant Christ is eternal -- He was victorious before the earth appeared, and will be victorious for eternity.

John's narrative is not entirely linear. There are some cases where he says something like "xyz is going to happen," then describes the results of xyz, after it has happened. 5:3-6 may be an example of this. It starts out by saying that no one can open the book (or scroll, in some versions) then we are told that the Lamb is honored as one who "opens the book." But 6:1 describes what happened, as if John had just seen it, when one of the seals is, in fact, opened.

11:3-11 is a better example of the "xyz phenomenon". The beast will kill the two witnesses, but then John tells us that they have already been killed, and have been resurrected. 14:17-20 is another example. An angel is told to act, then John writes as if the action had already taken place. 20:7-10 is an especially good example. We are told that Satan will be released from prison, then John tells us what happened when he was released. 21:5-7 may be another example. God is making all things new, but the rewards will come later, as if He hasn't done so yet.

21:1-2 seem to be about after the Final Kingdom is established, which, to us at least, is some time in the future, and was also even further into John's future. But John describes it as if he has seen it. 7:13-15 seem to be about what happened in the Great Tribulation, but also about the reward for those who went through it, after Christ's triumph.

Conclusion? God is outside of our time. To him, the past, the present, and the future are all accessible. John was given a vision of the present and the future, and did his best to describe it, but it was probably impossible for him to explain what he experienced in such a way that we can fully understand it.

What is the message of Revelation? There are at least two messages for us, related ones. "Be faithful" is one such, especially in the second and third chapters. "Christ is triumphant" is another one. These messages are more important than having a bullet-proof timetable for future events, events that are in our past, our present, and our future.

Thanks for reading!