"According to evangelical, Bible-believing postmillennialism, fallen man is utterly incapable of entering or advancing the kingdom of God in his own effort, wisdom, or accomplishment. God's kingdom comes not by human work, but by the redemptive mission of Jesus Christ (cf. Colossians 1:13-14) and according to the gracious power of the Holy Spirit. As Jesus said to Nicodemus: "Unless one is born again, he cannot see the kingdom of God" (John 3:3).
Postmillennialists believe that Jesus established the kingdom of God on earth during His first advent. Mark summarizes what Jesus preached: "The time is fulfilled, and the kingdom of God is at hand" (Mark 1:14). From His exorcism of demons Jesus authoritatively concluded: "the kingdom of God has come upon you" (Matthew 12:28). Jesus is now despoiling Satan's house (v. 29), as the kingdom slowly grows in the earth (Matthew 13:31-32), and every enemy is brought in submission under His feet (Hebrews 1:13; 10:13). He must reign until all opposition is defeated, and then He will deliver up the kingdom to the Father -- at His second coming, which is "the end" of history (1 Corinthians 15:24-25).
Postmillennialists believe that the victorious advance of Christ's kingdom comes about by means of the preaching of the gospel and the powerful work of God's Spirit in regeneration and sanctification. That is, it is the pursuit of the Great Commission, rather than the use of violence or military confrontation, which peacefully secures the widespread conversion of the world and brings it to obey all that Jesus has commanded (cf. Matthew 28:18-20).
However, the process through which the kingdom grows involves an intense spiritual battle, with its ensuing afflictions, persecutions, hardships and suffering for God's people. The ultimate victory which shall come through the struggle does not cancel the pain and sorrow which attends that struggle. The Apostle John spoke of himself as a "companion in the suffering and kingdom... that are ours in Jesus" (Revelation 1:9). Paul called on Timothy to "be a partaker of the afflictions of the gospel" (2 Timothy 1:8), realizing that "if we suffer [with Him], we shall also reign with Him" (2:12)." - Dr. Greg Bahnsen
I love being a Christian.