What is the kingdom of God?
The kingdom of God was at the center of Jesus’ teaching. He announced at the very beginning of His ministry, “The time is fulfilled, and the kingdom of God is at hand; repent and believe in the gospel.” (Mark 1:15)
What did He mean by the kingdom of God?
Jesus did not mean to announce that He had now established a new territory over which He was going to rule as we might think of the term “kingdom.” Jesus’ kingdom was not a domain won by conquest or purchased with money. In fact, Jesus said that His kingdom did not come in a visible way or with visible signs.
Now having been questioned by the Pharisees as to when the kingdom of God was coming, He answered them and said, “The kingdom of God is not coming with signs to be observed; (Luke 17:20)
Note that the kingdom of God is not something visible that can be seen with our eyes.
If Jesus’ kingdom was not visible, then what does it mean to say that it is “at hand” or that it has come?
Jesus’ kingdom comes when people submit to God’s rule and bow before Him as their king. This is why it is invisible. It is something that takes place deep in the heart of a man or woman and is not something that can be seen with the human eye.
This implies that no one before the coming of Jesus submitted to God’s rule.
In the Old Testament, people certainly did submit to God and follow Him. In this sense, the kingdom of God has always been. The term “kingdom of God”, however, has a specific meaning in the Bible. It is a term which refers to that time when the King would come to earth and begin to take back what He lost in the fall. (Gen 3) This was prophesied in the Old Testament and began with the coming of Jesus who is the King of the kingdom. It will be finished at the time of the great consummation when Jesus will deliver up the kingdom to the Father (1Cor 15:24) and history will come to an end. (Rev 21:6)
Why is this important for our understanding of the church?
It helps us understand the difference between the kingdom of God and the church. The kingdom of God is invisible while the church is visible.
How does the kingdom of God become visible to a human eye?
Because those who have submitted to God’s rule gather together in a group and worship their king. In this gathering, they become visible. This visible gathering is called “church”.
Where does the Bible teach this?
We can see this in the very term “church” or ecclesia or εκκλησια. This term was not a word that Christians invented. This word was commonly used in the Greco-Roman world for a gathering of any kind. This can be seen even in the Bible itself.
Where does the Bible use the word ecclesia or εκκλησια but not referring to Christians?
Recall that when Paul was in Ephesus, he provoked a riot because his preaching threatened the trade of the silversmiths. (Acts 19:25f) The mob which formed is called an ecclesia.
Some therefore cried one thing, and some another: for the assembly [ecclesia] was in confusion; and the more part knew not wherefore they were come together. … But if ye seek anything about other matters, it shall be settled in the regular assembly [ecclesia]. … And when he had thus spoken, he dismissed the assembly [ecclesia]. (Acts 19:32, 39, 41)
What can we learn from this usage of the word ecclesia?
That the central idea behind the word ecclesia is a gathering of some kind. In Acts 19:32, the gathering is an unruly mob; in Acts 19:39, the gathering is an orderly political body. In either usage, however, the word is used to refer to some kind of gathering. This is likely why the apostles chose to use this word to define the followers of Christ. Where as the kingdom of God is something invisible, the church is something visible and constitutes a gathering of Christian believers. The apostles often chose words which were already existence in the society of their time and used them to articulate Christian concepts; see Robertson for a long list of such words. source
Who are members of the church?
The members of the church are those who are citizens, we might say, of the kingdom of God. They are those who have submitted to the Great King, are living under His protection, and are obeying His laws.
If we want to understand the church, is it not appropriate to understand what Jesus teaches about the kingdom of God?
Yes, this is certainly correct. See here.