The Word of God is the gospel of the kingdom:
Matthew 24:14 And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come.
The correct interpretation of the Bible’s mysteries is the language of the kingdom of God:
Mark 4:11 And he said unto them, Unto you it is given to know the mystery of the kingdom of God: but unto them that are without, all these things are done in parables:
The nation of Israel and the N.T. churches were entrusted with the gospel of the kingdom (Word of God) and therefore they themselves became outward representations of the kingdom of God to the people of the earth:
Matthew 21:43 Therefore say I unto you, The kingdom of God shall be taken from you, and given to a nation bringing forth the fruits thereof.
(Note: the above statement is speaking to Israel. The kingdom of God was taken from them and given to the N.T. church indicating that the N.T. corporate church was also the kingdom of God).
Of course we are living at a time when God has brought judgment on all the world’s churches and has ended His relationship with them. Therefore the churches of the world no longer represent the kingdom of God to the inhabitants of the earth. Their time of representation has come to a close.
The Bible also indicates that when someone became saved they also became a citizen of the kingdom of God:
John 3:3 Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.
4 Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother's womb, and be born?
5 Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
A person must be saved to enter into the eternal kingdom of God (but there was no need of actual salvation to enter into the earthly outward representation like Israel/corporate church).
Luke 17:20 And when he was demanded of the Pharisees, when the kingdom of God should come, he answered them and said, The kingdom of God cometh not with observation:
21 Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you.
No one can see the wind or see the inward change in a person that God has saved. Salvation grants a person access into the kingdom of heaven.
Colossians 1:13 Who hath delivered us from the power of darkness, and hath translated us into the kingdom of his dear Son:
The eternal kingdom of God involves understanding God’s Word spiritually (knowing the mysteries, or the language of the kingdom of God) but more than that it is salvation of the soul.