The following post is of course in no way meant to be an exhaustive treatment of eschatology (the study of last things). I would refer the reader to the following books before I give my shpiel:
Postmillennialism: An Eschatology of Hope, by Keith Mathison. Although I would disagree with Mathison's partial preterism, otherwise I think the book is excellent. He argues that postmillennialism is consistent with Reformed theology, and considers various passages of Scripture in both testaments.
The Victory of Christ's Kingdom, by John Jefferson Davis. This book is an excellent introduction to the postmillennial eschatology.
Three Views on the Millennium and Beyond, with Kenneth Gentry presenting the postmillennial view. One thing I appreciate much is his response to Robert Strimple, a Reformed amillennialist. Gentry says that amillennialism stops short of postmillennial conclusions. This truth was one thing which led my wife and me from amillennialism to postmillennialism as well.
--Greg Bahnsen's article, "The Prima Facie Acceptability of Postmillennialism." I believe it can be found for free at www.cmfnow.com, but it is also a chapter in his book, Victory in Jesus: The Bright Hope of Postmillennialism. I think this article is a good article to whet your appetite and prepare you for further study.
Now, without further ado, let us begin our feast.
POSTMILLENNIALISM IS NOT SO MUCH ABOUT ESCHATOLOGY AS IT IS ABOUT CHRISTOLOGY
Postmillennialism is that view of last things which holds that the gospel of Christ will have overwhelming success in history, and that it will have converted the majority of mankind at some point before Christ returns. Most postmillennialists, as do I, also hold that God has elected to eternal life a multitude more than those He has reprobated.
Why does the Scripture hold this as true? This view is more about how we view Christ's kingship. Christ has been crucified, and He has risen in vindication. He now sits at the right hand of the Father in heaven. This is a place of authority and power.
In the Great Commission, our Lord says that, "all authority in heaven and on earth [italics mine] has been given to Me. Therefore go and disciple the nations." The Great Commission is concerned with people groups, and we are told in Matthew 24 that before our Lord returns, this gospel of the kingdom must be preached as a testimony to all nations, and then the end will come.
This is connected to Psalm 110, where God says to Christ to "sit at My right hand until I make your enemies a footstool for Your feet." This cannot be talking about the future only, because in the same passage God tells Christ to "rule in the midst of Your enemies."
In the book of Revelation Christ conquers by the sword in His mouth, which is symbolic of the gospel preached. He goes out on a white horse and conquers the nations by the power of the Sword of God, that is, the gospel preached and applied by the Holy Spirit.
But all of this has its source in the promise that God made with Abraham. He promised he would be the father of many nations, and that his children would be as the dust of the earth. We are told in Galatians 3 that this is fulfilled in Christ, and in all who are united to Him by faith.
This is why David can say in Psalm 22 that "all the ends of the earth will remember and turn to the Lord, and all the families You have made will worship You."
And we are told in Romans 11 that God's purpose in temporarily casting Israel aside is for the gospel to conquer the Gentile nations, at which Israel will become jealous, and then they too will turn to the Lord, which will spark an even greater host of conversions.
This, of course, is only a start for the study of God's promises. But Christ has come to destroy the works of the devil, and He has bound the strong man, so now He will spoil his house. Notice that Satan's kingdom will be spoiled, not just hit a little here and a little there. The gates of hades are no match for the onward march of the church of God. They will not stand up under the onslaught of Christ's church.
God is in the business of doing things which seem impossible to us. He gave Sarah a baby in her old age. He promises to cause us to persevere.
He also promises that His gospel will conquer.
Praise be to our covenant-keeping God!