The question begins with a very common and very false presumption that the words written almost 2,000 years ago to a people who are no longer living on this earth are yet to occur. Christ was the revealer, the speaker of this prophesy, and He revealed something to John which "must shortly come to pass".
"The Revelation of Jesus Christ, which God gave unto him, to shew unto his servants things which must shortly come to pass; and he sent and signified it by his angel unto his servant John:" (Rev. 1:1, KJV)
The presumption for most readers is that the word "shortly" means soon to the person reading it. So for 20 centuries each student reading the prophesy expects "shortly" to be their generation? How is that a prophesy? False prophets were to be stoned, yes?
"When a prophet speaketh in the name of the Lord, if the thing follow not, nor come to pass, that is the thing which the Lord hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him." (Deu. 18:22, KJV)
Many people have turned away from God and from Christ because they have been taught to believe the book of Revelation was telling their generation Christ was coming soon, and when He didn't appear they concluded that He had lied. They made the same mistake of making the same false presumption.
The key is first audience perspective. Who was the prophet, and to whom was He speaking? Because those people to whom the prophet was speaking heard the same words..."must shortly come to pass".
If you were to find your grandmother's diary after she died, one she had written 70 or more years ago, and in it she wrote of her dream to travel to Paris "soon", in a year of so, would you think she had yet to travel to Paris? When you read the word "soon" does it mean soon from the time you read it, or from the time she wrote it? When do you start counting time, from the moment it was written or the moment you read it decades later?
First audience perspective demands that the "time" words and time texts of the scriptures be applied to those who heard and read those words. The ones who heard this prophesy, the ones to whom John was sent to prophesy again (Rev. 1:3-4) were the saints of the assemblies of Christ, the "ecclesia" of the first century A.D.
"Blessed is he that readeth, and they that hear the words of this prophecy, and keep those things which are written therein: for the time is at hand. 4 John to the seven churches which are in Asia: ..." (Rev. 1:3-4, KJV)
So, if we who are studying this prophesy place the time correctly for the first audience in the first century A.D., then these events are our history. Only then can we pinpoint many of the events that were symbolized in this vision.
Christ was the prophet of this vision, and He revealed it to John to tell the seven churches which existed in Asia. Why is it so hard then to understand that the time frame of this prophesy was during the existence of those same seven churches / assemblies to whom John was sent?
If the time frame of this prophesy is yet future, then is John still living and is he yet to prophesy to these seven assemblies of Christ?
The book ends with five most emphatic statements of the "soon" and "at hand" nature of this prophesy for those who heard it in the first century A.D.
Rev. 22:6, "...which must shortly be done." (KJV)
Rev. 22:7, "Behold, I come quickly..." (KJV)
Rev. 22:10, "...for the time is at hand." (KJV)
Rev. 22:12, "And, Behold, I come quickly..." (KJV)
Rev. 22:20, "...Surely I come quickly..." (KJV)
These time statements are often argued away by turning them into the nature and method of His coming; saying that when He came it would be done quickly. That is a rationalization to make an accommodation for a belief system, and twists the meaning of the scriptures to do so.
Christ told John He was coming quickly while John yet lived, which fulfilled His earlier statement before His crucifixion that John would live to see His coming (John 21:22).
Christ told the disciples that they would not finish going through the cities of Israel before He came (Matt. 10:23).
Christ told the Pharisees that the axe was already laid to the root of the tree (Matt. 3:10).
Christ told the disciples that their days were the days of vengeance that all things would be fulfilled (Luke 21:22).
Christ told the disciples that some who were standing before Him would live to see Him coming in His kingdom (Matt. 16:28; Luke 9:27).
Christ told the high priest Caiaphas that Caiaphas would see Him coming in the clouds of heaven (Matt. 26:64; Mark 14:62).
Coming in the clouds...judgment language as used in the OT for judgment upon a wicked nation (Job 22:14; Psa. 104:3; Dan. 7:13; Nah. 1:3), and as used again in Rev. 1:7.
"Behold, he cometh with clouds; and every eye shall see him, and they also which pierced him:..."
Every eye saw Him in the result of His judgment that came upon the remnant of Israel in the destruction of Judea, Jerusalem and their temple in AD 70. Those who had pierced Him were living to see that judgment coming, therefore the time of His coming happened while they yet lived.... in the first century A.D.
There is much more evidence the scriptures reveal for this first audience perspective that these things have already happened long ago at my blog ShreddingTheVeil. But this question asks for several meanings of the symbols in Rev. 8:8 which would take much time and many words to support for they are based upon those same symbols as used in the OT.
The sea was a symbol of the pagan nations which surround the "pleasant land" of Israel / Judea (Jer. 3:19; Dan. 8:9) as being an opposite natural feature of the "earth" of Israel.
A mountain was used for a nation or kingdom, and God's mountain stands for God's kingdom (Isa. 11:9; 56:7; 57:13; 65:25; 66:20; Ezek. 20:40; Dan. 9:16, etc.). That this mountain was burning indicated the fire of God's judgment had come upon it. Being cast into the sea indicated that it had been thrown down among the pagan nations. It was the earthly Mt. Zion of Jerusalem that was cast down among the pagan nations.
The third part of the creatures that were in the sea, or pagan nations referred to a part of the people of those nations being killed when that great Mountain was thrown down from its prior station. They were killed in the battle of the Roman-Jewish war of 67-70 AD when the temple at Jerusalem was destroyed.
The judgment, God's fire was the coming of Christ to judge Judea, Jerusalem and to destroy that temple for all those who had crucified Christ and to establish His kingdom over all the kingdoms of the entire earth. It was the establishment of the true kingdom of God, and Christ rules at His right hand in that kingdom. He has been ruling at the right hand of the Father for almost 2,000 years.
Revelation is the record the Holy Spirit has given us so that we can know assuredly that Christ won that battle over the wicked ones of Jerusalem who crucified Him, and that He reigns over the entire world. It is also our assurance that He judges wicked nations that do not walk with Him, even of His own people. It is a record of the establishment of His spiritual city and His spiritual kingdom for all those who are in Christ.
The current teaching of Revelation as a yet future prophesy makes Christ out to be a liar, and a false prophet by denying the "soon" and "at hand" nature of this prophesy to the saints of the first century AD to whom this prophesy was given. It denies the existence of His kingdom, and of His reign / rule.
The futurist view was contrived for a political reason to support a political agenda to re-establish a political state of Israel in 1948 for the benefit of a certain group of people who had purchased much of the land in Palestine in the late 1800's, and the psyop has succeeded very well in deceiving a great many Christians.
"The Time of His Coming" here
"Frequent Mistakes - Part III: The Last Day here
"Frequent Mistakes - Part VI: The End of The World, or ? here
"It's Not The End of The World Part VI: The Zionist & Jesuit Deceit" here
