The Kingdom of God resides with God in heaven. In this age, the god of this world is Satan the Devil (II Corinthians 4:4), placed here by God in ages past to govern the earth (compare Isaiah 14:12-15; Ezekiel 28:12-17; Matthew 4:8-9; Jude 6). When Satan and his angels sinned, they rejected the government of God and established their own on the earth, where they remain to this day. When God created man, Adam and Eve chose to follow Satan's way, condemning all humanity to live under the Devil's influence until the Savior opened the way to restore God's government on the earth.
Presently, however, only those whom God calls and works with have voluntarily submitted to God's rule. These people, known as true Christians, have been born again—spiritually regenerated as a new creation—into a relationship with God and Christ and spiritually inducted into the Kingdom of God (Ephesians 2:5-7). Paul writes that "our citizenship is in heaven, from which we also eagerly wait for the Savior, the Lord Jesus Christ" (Philippians 3:20). He likens us to "ambassadors for Christ" (II Corinthians 5:20), emissaries of a foreign government, subject to its laws and methods.
However, Christians have not yet fully entered into God's Kingdom; they are still flesh and blood, which "cannot inherit the kingdom of God" (I Corinthians 15:50). This will occur at the resurrection from the dead when Christ returns to this earth to restore God's government, bringing peace, prosperity and refreshing to all (Isaiah 9:6-7; Acts 3:19-21; I Corinthians 15:22-28). The Kingdom of God will then be a real, physical entity on the earth, ruled by Jesus Christ with the help of His brethren, the resurrected, immortal saints (Revelation 5:10; 20:4-6).