The following is something I cobbled together in response to a friend on Facebook. It seemed good enough to warrant posting here.
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When Jesus ascended into heaven, He proclaimed that all authority in heaven and earth had been given to Him - Matthew 28:18. In other words, since the first century, Jesus has been King, not just of heaven, but of earth also. On this basis, He then told His disciples to go make disciples of all the nations. He gave no hint of this being a failing mission. Quite the contrary, the fact that He gave them the order the way He did implied success.
If Jesus has been given all authority in heaven and on earth now, then that means there is no future authority to add to Him. And if this is true, then that means the thousand years referred to in Revelation 20:1-6 doesn't refer to a period later in history, it refers to right now. It began in the first century AD. The number 1000 is used symbolically throughout Scripture (God owns the cattle on a thousand hills, a day with the Lord is as a thousand years, etc.), and in this case, it is symbolic of Christ's entire reign from His ascension into heaven until His second coming.
Eventhough Christ is reigning now, there is still evil in the world. There are those who are still His enemies. Christ will reign until the time comes when all His enemies will have been put under His feet (Hebrews 10:13; 1 Corinthians 15:25), that is, until they are finally all conquered. That will be the end of the world, the end of history (1 Corinthians 15:23-28). We are to participate with Him in the conquering of the world, through weapons not of flesh and blood (Ephesians 6:10-20). One might more properly say that He is conquering the world through us. Jesus said that the gates of Hell would not prevail against His Church (Matthew 16:18). That is not the image of a weak, defeated Church, but one that is strong and conquering. The Church is not on the defensive, but is on the offensive, storming as it were the very gates of Hell, which can't prevent it. Christ is reigning, and will conquer all His enemies (Psalm 2, Psalm 110). And every knee will bow to Him, whether it wants to or not (Phil. 2:9-11). Those who submit to Christ will be part of the many nations God promised Abraham he would be a father of (Gen. 17:4-8). They will receive the blessings of the Abrahamic Covenant, which is fulfilled in Christ (Romans 4:9-13). God promised He would bless all the families of the earth through Abraham, He has done that through Christ (Gen. 12:3). All who have faith in Christ are children of Abraham (Galatians 3:7-9), and inherit not just the land of Israel, or even just the planet earth, but the entire universe (Romans 4:13 - the word usually translated "world" is actually "kosmos" in the Greek, or "cosmos", which means exactly what it says - it means "universe").
The kingdom then, is something that will come into its fullness gradually. It began with Jesus ascension and will continue to grow until He returns. Jesus spoke of this in the Parables of the Mustard Seed and the Leaven (Matthew 13:31-33). Just like the sanctification of an individual Christian, so it is with the sanctification of the whole world, if you will. If you stare at it at any one point and time, you can't necessarily see it. But it's still happening, just very slowly. You can stare at the mustard seed in the ground right after you've planted it, and it looks like nothing is happening. But something is happening - it's just invisible to you. Only a few months later will you see its progress. The coming of the kingdom is not something that can be observed (Luke 17:20). If it were an immediate, catastrophic event, that wouldn't be true. Jesus speaks the same way in the Parable of the man who sowed seed (Mark 4:26-28).
The Kingdom promised is to more than just Israel - it is to all the nations (Isaiah 2:2-4; Is. 27:6; Is. 56:3-8). There will be cultural ramifications of the spreading of the Gospel, such as in a growth of peace (Is. 2:4; Is. 11:6-9). Physical and material blessings will accompany the spiritual blessings that flow to the nations (Is. 35:1-10; Is. 41:17-20). We are given images of these things in Scripture, but the exact shape they will take only time will tell. It is common for people to go to these passages in Isaiah, and assume that because they don't see them fulfilled right now, that they won't be fulfilled during this age. But, as we've said, the kingdom comes gradually. And since the kingdom comes gradually, so do the blessings that are a part of it. Will there ever be a time during this age in which the things mentioned in Isaiah 11:6-8 literally take place? Or are they merely symbols? The latter may be true, but I see no reason why the God of the universe couldn't make them literally take place in this age.
