It is the most important question about the kingdom of God.
Some people believe the Kingdom is just a synonym for heaven. Others believe the Kingdom is the Church. Both are only partly right.
One of Jesus’s teachings about the Kingdom was a parable about wheat and tares. Matt. 13:24-30.
Jesus said the wheat represented the sons of the Kingdom, the tares represented those who were not submitted to God but His enemy, and that both would grow together until the end when God would remove the tares “out of His kingdom.” Matt. 13:36-43.
Now, I’m no theologian, just a simple lawyer, but if God had to take non-Christians out of His kingdom, then the Kingdom cannot be heaven, because non-Christians don’t go to heaven, and the Kingdom can’t be the Church, for the same reason. The true Church consists only of believers. That must mean the kingdom of God is something different than heaven or the Church.
What the Kingdom is is found in the word Jesus chose to describe it: It is a kingdom. And the thing without which a kingdom would not be a kingdom is a king who reigns. The kingdom of God then is the reign of Jesus.
Jesus said his kingdom was like a mustard seed which a man planted in his garden. It is smaller than all the other seeds, but when it is full grown it is larger than all the other garden plants and becomes a tree, and the birds of the air nest in its branches. Matt. 13:31-32. If you have a reference Bible you will note the phrase “birds of the air nest in its branches” is a reference to Daniel 4:12 and Ezekiel 31:6 and refers to pagan nations. In other words, Jesus was saying that His reign would start small (which it did with twelve disciples) and would grow to such an extent that even non-Christians would come under its shadow to enjoy its benefits.
So, the kingdom of God includes heaven because Jesus reigns in heaven, and it includes the Church insofar as people in the Church submit to the reign of Jesus in their lives, but Jesus’ reign extends beyond heaven and the Church such that non-Christians can be under its influence (in a sense “in it”) on the earth without inheriting it.
The kingdom of God is the reign of King Jesus. And where King Jesus reigns, there is the kingdom of God. But I better stop there because now I am getting into the “where” of the Kingdom, which is the next post. GS