It has nothing to do with the timing of the millennium. It has to do with God’s Word!
Interpreting God’s Word
There are many that believe that the timing of the Millennial Kingdom is a third tier issue and dismiss those that believe differently as holding onto an issue of little consequence too tightly. They avoid entirely the fact that at the heart of the millennial issue is a first tier issue. At the very heart of the issue is the method of interpreting Scripture. The issue is quite clearly the very Word of God and not some “third tier” issue. Pre-millennialists follow a “grammatical-historical” or literal interpretation. Amillennialists use a spiritualizing method with prophesy or with any Scripture that they need to uphold their millennial view.
The doctrine of the clarity of Scripture teaches that the meanings of Scripture can be clear to the ordinary reader. The very fact that God uses His Word to communicate to His people indicates that His intent is that they understand it. The Word of God is the very cornerstone of our faith and practice. God did not intend that we needed a magisterium or a theologian with multiple doctorates to teach us what God clearly wanted us to understand.
Augustine was the first “theologian” that formulated the doctrine that came to be known as amillennialism. Augustine refined a method used by the allegorical school of interpretation which was heavily used in the Eastern Church. Augustine was to give a more moderate application of the allegorical principle of interpretation and referred to it as spiritualizing Scripture. In general, he held that only prophecy should be spiritualized and that in the historical and doctrinal sections of Scripture the “grammatical-historical” or literal method should be used.
It is helpful to note that Augustine was a revisionist and a revisionist that would change the direction of Church doctrine. The overwhelming view of the first and second century Church was a literal approach to prophecy and a pre-millennial view of the Millennial Kingdom. The overwhelming view of the Church from Augustine on was that the Church was the arbiter of what Scripture meant. The history of the Church and it’s control of Scripture from this point on is undeniable. Scripture was not available outside the control of the Church and the Bible in the vernacular of the people was prohibited. The doctrines of purgatory, transubstantiation, sale of indulgences, pilgrimages, the excessive veneration of saints, clerical celibacy all would be adopted by a Church that long since had abandoned a literal view of Scriptures. With the introduction of the allegorical or spiritualization method of interpretation it is clear the door was opened to bad doctrine. But this was not always so.
Leon Wood in his book The Bible and Future Events: An Introductory Survey of Last-Day Events states “There is general agreement among scholars that the view of the early church was premillennial. That is, Christians held that Christ would rule over a literal, earthly kingdom for one thousand years, assisted by raptured saints. No church fathers of the first two centuries are known to have disagreed with this view. The following may be listed as those who favored it: from the first century, Aristio, John the Presbyter, Clement of Rome, Barnabus, Hermas, Ignatius, Polycarp, and Papias; from the second, Pothinus, Justin Martyr, Melito, Hegisippus, Tatian, Irenaeus, Tertullian, and Hippolytus. Though not all of these set forth their view with the same clarity, some gave very clear indications of their premillennial position. Two of these are particularly significant. First is Papias (A.D. 80-163), who not only stated his own view clearly but added that his view was held also by the apostles Andrew, Peter, Philip, Thomas, James, John, and Matthew. Papias was in a position to know early church thinking, for Irenaeus says of him that he was one of John’s hearers and was intimate with Polycarp. It may be concluded that, in the early church, a common view was that Christ’s apostles were themselves premillennial. Second is Justin Martyr, of the second century, who not only set forth his own premillennial position but added that this was the view of all Christians who were orthodox.”
With this in mind let’s review the difference that the Pre-Millennialist and the Amillennialist would use in interpreting Scripture.
The Pre-Millennialist Approach to Biblical Exegesis – Literal-Historical Interpretation
This is the method clearly held by the early Church. This is a method that God intended so that His people would receive His Word with no ambiguity. This method of exegesis or Biblical interpretation holds that we interpret the Bible according to its normal, literal or grammatical and historical meaning. In other words, we understand the words and sentences according to the way they were normally used by the speakers of the language. It also means that we understand the words and sentences in their historical context. Using the grammatical-historical method means we interpret the Bible in light of:
The original languages – The Bible was not originally written in English. The Old Testament was mainly written in Ancient Hebrew with the exception of Daniel and Ezra being written in Aramaic. The New Testament was mainly written in Koine Greek, the popular form of Greek at that time. This method of interpretation relies heavily on understanding the meaning of the words and sentences in the languages in which they were originally written.
The historical and cultural context – The various authors of the books of the Bible lived at a time in history and in a culture that was unique to the time that they wrote in. This method takes into consideration the context of that time both in terms of the history and culture of the author and to whom he was writing.
The literary genres – The word genre means kind. Literary genre simply means different kinds of literature. Poetry, for example, is a different kind of literature than a historical narrative, and therefore there are different principles for understanding it. The grammatical-historical method of interpretation takes this into account.
These are some of the basic factors that are taken into account by those that interpret the Bible in a literal sense.
Amillennial Approach to Biblical Exegesis – Spiritualizing combined with Literal
Amillennial use of the literal method – The amillennial method of interpreting Scripture is correctly defined as the spiritualizing method. It needs to be noted that this method it not universally applied to all Scripture. Amillennialists in fact predominantly apply it to prophecy and use the literal method of interpreting most other Scriptures. In other words, amillennialists use two methods of interpretation, the spiritualizing method for prophecy and the literal method for most other Scriptures.
The problem arises is that if the interpreter has a choice of method in interpreting Scripture, a large door for difference of opinion is opened. The general designation of prophecy as the field of spiritualization is by no means definite. In fact, amillennialists who are conservative interpret many prophecies literally and, on the other hand, use the spiritualizing method in some instances where prophecy as such is only remotely involved. The modern liberal scholar, who is also an amillennialist, feels free to use the spiritualizing method rather freely in areas other than prophecy whenever it suits his fancy, and being bound by no law of infallible inspiration need not be concerned if the result is not consistent. 
A good example of how this spiritualization of Scripture can twist Scripture is Revelation 20:1-3. The Scripture clearly reads: “Then I saw an angel coming down from heaven, holding in his hand the key to the bottomless pit and a great chain. And he seized the dragon, that ancient serpent, who is the devil and Satan, and bound him for a thousand years, and threw him into the pit, and shut it and sealed it over him, so that he might not deceive the nations any longer, until the thousand years were ended. After that he must be released for a little while.”
Amillennialists interpret this as Satan was bound at the cross, but his “binding” is in such a way that he can still deceive. Besides the timing of the binding it totally contradicts that he is bound so “he might not deceive the nations any longer.” One noted amillennialist is William Hendriksen who uses the analogy that Satan is like a dog “bound with a long and heavy chain [who] can do great damage within the circle of his imprisonment”. Others explain Satan’s presence on earth today by using the imagery that Satan is on a leash, apparently a very long least. Scripture does not say that.
1 Peter 5:8-9
“Be alert and of sober mind. Your enemy the devil prowls around like a roaring lion looking for someone to devour. Resist him, standing firm in the faith, because you know that the family of believers throughout the world is undergoing the same kind of sufferings.”
2 Corinthians 4:4 – Paul in this passage refers to Satan as the “god of this age”.
The god of this age has blinded the minds of unbelievers, so that they cannot see the light of the gospel that displays the glory of Christ, who is the image of God.
Ephesians 6:10-17 – In this passage it seems Paul didn’t get the memo about Satan being bound.
The Armor of God
“Finally, be strong in the Lord and in his mighty power. Put on the full armor of God, so that you can take your stand against the devil’s schemes. For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms. Therefore put on the full armor of God, so that when the day of evil comes, you may be able to stand your ground, and after you have done everything, to stand. Stand firm then, with the belt of truth buckled around your waist, with the breastplate of righteousness in place, and with your feet fitted with the readiness that comes from the gospel of peace. 16 In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one. Take the helmet of salvation and the sword of the Spirit, which is the word of God.”
1 Thessalonians 2:18 – Paul continues to just not get it.
“For we wanted to come to you—certainly I, Paul, did, again and again—but Satan blocked our way.”
These passages do not depict a being who has been bound and shut up in a pit. Jesus’ casting out of demons in Matthew 12:22-29 is evidence that He had the authority to bind Satan. But as the multiple New Testament texts have already affirmed, this binding did not take place at Christ’s first coming. With the aforementioned Scriptures clearly defining that Satan is loose in the Church age it becomes clear that the Millennial Age is not upon us. For a more in depth understanding of the binding of Satan please refer to my post: Has the Devil been bound in the Church Age?
Another clear and unambiguous reading of Scripture is the timing of the Millennial Kingdom. For a better understanding of the gymnastics that amillennialists need to get their kingdom before the Second coming read my post on: John’s the Revelator’s Great Editing Error. Meanwhile I will give you a quick review of their doctrine of Progressive Parallelism.
“Then I saw the beast and the kings of the earth and their armies gathered together to wage war against the rider on the horse and his army. But the beast was captured, and with it the false prophet who had performed the signs on its behalf. With these signs he had deluded those who had received the mark of the beast and worshiped its image. The two of them were thrown alive into the fiery lake of burning sulfur. The rest were killed with the sword coming out of the mouth of the rider on the horse, and all the birds gorged themselves on their flesh.
And I saw an angel coming down out of heaven, having the key to the Abyss and holding in his hand a great chain. He seized the dragon, that ancient serpent, who is the devil, or Satan, and bound him for a thousand years. He threw him into the Abyss, and locked and sealed it over him, to keep him from deceiving the nations anymore until the thousand years were ended. After that, he must be set free for a short time.
I saw thrones on which were seated those who had been given authority to judge. And I saw the souls of those who had been beheaded because of their testimony about Jesus and because of the word of God. They had not worshiped the beast or its image and had not received its mark on their foreheads or their hands. They came to life and reigned with Christ a thousand years. (The rest of the dead did not come to life until the thousand years were ended.) This is the first resurrection. Blessed and holy are those who share in the first resurrection. The second death has no power over them, but they will be priests of God and of Christ and will reign with him for a thousand years.”
The early Church would not have read Revelation with chapter and verse notations. They would have read Revelation as you see it as presented above. As it reads these verses flow naturally together as one continuous message. The early Church would have understood it as it was meant by the Holy Spirit to be understood. Christ returns and the kings of the earth gather to defeat Him. The beast is then captured along with the false prophet and both are thrown into the fiery lake of fire. The rest of the opposition to Christ are then killed. Immediately following this John tells us that he saw an angel coming down out of heaven. This angel has a key to the Abyss and holds a great chain in his hand. John then tells his reader that the Angel “seized the dragon, that ancient serpent, who is the devil, or Satan, and bound him for a thousand years.” He then proceeds to describe that which was revealed to him. The righteous would be resurrected and reign with Him for one thousand years.
We now get to Progressive Parallelism. This is the methodology used to put Christ’s Millennial rule on earth before Christ’s Second Coming and not after as the text clearly states. Anthony Hoekema, one of the leading proponents of the Progressive Parallelism puts it this way:
“The premillennial interpretation of these verses understands them as describing a millennial reign of Christ on earth which will follow his Second Coming. And it is true that the Second Coming of Christ has been referred to in the previous chapter (see 19:11-16). If, then, one thinks of Revelation 20 as setting forth what follows chronologically after what has been described in chapter 19, one would indeed conclude that the millennium of Revelation 20:1-6 will come after the return of Christ. As has been indicated above, however, chapters 20-22 comprise the last of the seven sections of the book of Revelation, and therefore do not describe what follows the return of Christ. Rather, Revelation 20:1 takes us back once again to the beginning of the New Testament era.” The Bible and The Future, pp. 226-27
To clarify: Amillennialists do not view the events of Revelation from a chronological or sequential perspective but, instead, see the book as describing the church age from several parallel perspectives that run concurrently. There are according to this theory seven total parallel ages that divide up the book. The seventh parallel age would be Revelation chapters 20 through 22. These chapters are then posited to have taken place at Christ’s first coming. Thus the binding, for instance, of Satan ushered in the millennial kingdom at the time of Christ’s first coming not after His second coming. This does leave us with several questions. If the Holy Spirit meant the last to be first why did he inspire John to write the first to be last. The other question that comes to mind is the doctrine of the clarity of Scripture. Where were the amillennialist scholars and theologians to explain this to the early Church? Do we really believe that the Holy Spirit intended these passages to be this confounding or do we hold to the doctrine of the clarity of Scripture? Wasn’t it God’s intent that His Word to His people be understood?
Is that clear? I didn’t think so.
 Amillennialism as a Method of Interpretation, Theological Journal Library