George Ladd in Wayne Grudem's Systematic Theology mentioned this, which was interesting and good to consider, as talking about the Kingdom of God can be a confusing idea, or at least, for me anyways.

He states that it is "primarily the dynamic reign or kingly rule of God and derivatively, the sphere in which the rule is experienced. "

"In Biblical idiom, the Kingdom is not identified with its subjects. Ex: the church is the community of the Kingdom, but never the kingdom itself. Jesus' disciples belong to the Kingdom as the Kingdom belongs to them; but they are not the Kingdom.

The Kingdom is the rule of God; the church is a society of men. I see the church as a vessel or instrument through which Christ Jesus works through us to accomplish those things of His Kingdom. Ladd states that we are the custodian of the Kingdom (for the church has been given the keys fo the kingdom of heaven: Matt. 16:19)

"Jesus and the early Christians preached that the kingdom of God was near, not that the church was near, and preached the good news of the kingdom, not the good news of the church: Acts 8:12; 19:8; 20:25; 28:23, 31.)

The Kingdom creates the church (for as people enter  into God's kingdom they become joined tothe human fellowship of the church.)

 Let us not give ourselves too much power and think of the church as being God's kingdom.

 Jim Cannon, my pastor back home says that within any kingdom, three things exist: the realm, the ruler and the people.

With the Kingdom of God,it's realm is heaven, it's ruler is God, and it's people are the children of God.

The Kingdom of the Devil has it's realm as the world, it's ruler is the devil, and it's people are the children of the devil. By "world" what is meant is.... "the organized system of human civilization that is actively hostile to God and alienated from God." C.J Mahaney, Worldliness, Crossway, 2008. p. 26