Here in Eph 5:5....The kingdom of Christ is the coming millennium...
These verses speak much on it...
Rev. 20:4, 6
And I saw THRONES, and they sat upon them, and judgment was given to them. And I saw the souls of those who had been beheaded because of the testimony of Jesus and because of the word of God, and of those who had not worshipped the beast nor his image, and had not received the mark on their forehead and on their hand; and they lived and REIGNED with CHRIST for a thousand years.
6 Blessed and holy is he who has part in the first resurrection; over these the second death has no authority, but they will be priests of God and of Christ and will reign with Him for a thousand years.
Matt 16:28
Truly I say to you, There are some of those standing here who shall by no means taste death until they see the Son of Man coming in His kingdom.
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Its also the kingdom of God as seen here...These two verses are from the same chapter of Matthew 13. Imagine that
Matt. 13:41
The SON of Man will send His angels, and they will collect out of HIS KINGDOM all the stumbling blocks and those who practice lawlessness
Matthew 13:43
Then the righteous will shine forth like the sun in the KINGDOM of their FATHER. He who has ears to hear, let him hear.
Also these two verses shows that the Kingdom of God the Father is the Kingdom of the Son of Man.
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The believers have been regenerated into the kingdom of God, and they are in the church, living in the kingdom of God today.
John 3:5
Jesus answered, Truly, truly, I say to you, Unless one is born of water and the Spirit, he cannot enter into the kingdom of God.
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The other reference to the Kingdom of God and Christ can be seen here as well.
Revelation 12:10
And I heard a loud voice in heaven saying, Now has come the salvation and the power and the kingdom of our God AND the authority of His Christ, for the accuser of our brothers has been cast down, who accuses them before our God day and night.
It is called the Kingdom of God, but the Authority of this Kingdom is of His Christ. A Kingdom cannot be a Kingdom without the necessary Authority to carry it. Christ is fully qualified to be this Authority.
This also shows the Oneness of the Father and the Son in the Divine Trinity.
Awesome question sister.
Ty for asking about it.