In explaining the meaning of the Parable of the Wheat and Tares to His disciples, Jesus said He would send his angels to “gather out of His kingdom all stumbling blocks, and those who commit lawlessness, and will case them into the furnace of fire…” (Matt. 13:41-42). Jesus made a similar statement in the Parable of the Dragnet. (Matt. 13:47-50). If the kingdom of God is the same as heaven, Jesus’ statements make no sense because non-Christians will not enter heaven.
Jesus’ description of the kingdom of heaven only makes sense if the kingdom of heaven is an administration with an earthly presence such that non-Christians can be “in” it on the earth but denied entrance into heaven and eternal life.
When the Bible employs the phrase “kingdom of heaven,” it is referring to the origin of the kingdom, not its location. This is like referring to the Apostle Paul as “Paul of Tarsus.” Jesus told Pontius Pilate that He indeed was a king, but that His kingdom was not of this world or realm. (John 18:36). Its origin was from another realm, namely the spiritual realm.
The kingdom of God is not the same thing as the Church or heaven. It includes both, but its earthly boundaries extend beyond the boundaries of both.