What is the Gospel of the Kingdom?
The basic framework of postmillennialism begins with understanding the nature and starting point of the Kingdom. What is the Kingdom of God? Where is it? When is it? The answers to these questions drive the resulting outlook and belief regarding Eschatology. And more importantly, the resulting response to the belief will either be an advance upon the world, or it will be a retreat from the world.
Christians Are Called To Win The World
What is the calling of the Christian? If it really is to advance a Gospel Culture, then our calling is to win the world by declaring the truth of God's Kingdom in every area of life. Specifically, it is to take every area of though and life captive to the obedience of Christ. If our LORD declares conquest, then what right have we to call a truce, give ground, or worse yet, wave the white flag? What we believe about the battle will not change that result, but it will demonstrate what kind of soldier we are.
Christ as King
What does it really mean that Christ is King? Is this just a trite title we give him? Does it merely reference him as Lord and God? Or does it imply a promised outcome? That is, the rule of God's righteousness and justice in the earth. Does Christ have all authority in heaven and on earth? Has he not promised us to pray that his kingdom come, and his will be done on earth, as it is in heaven?
Optimism in Action
What does a postmillennial perspective of the world look like? What does an outlook of optimism give a culture? What we believe about the future, will determine at least with what veracity we pursue our obedience to Christ. If we believe the world is going to end any moment, then we will save souls, and relegate culture to the garbage bin. If we believe that the church of Christ will never overcome the world, or defeat the the gates of hell, then we will mysticize the victory of Christ in the world. Only with an optimistic view of the future can we truly maintain a consistent hope for victory and advancement of Christ's Kingdom in the world and live out that hope in a concrete way.