The expression "kingdom of God" must be taken in its context to decide just what the Spirit of God has before Him in the passage of Scripture in which it is found.
We have the setting up of the kingdom of God in its heavenly aspect in Luke 13:28,28There shall be weeping and gnashing of teeth, when ye shall see Abraham, and Isaac, and Jacob, and all the prophets, in the kingdom of God, and you yourselves thrust out. (Luke 13:28) and in its earthly aspect in Mark 15:4343Joseph of Arimathea, an honorable counsellor, which also waited for the kingdom of God, came, and went in boldly unto Pilate, and craved the body of Jesus. (Mark 15:43); also Luke 17:20;19:11;21:3120And 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: (Luke 17:20)
11And as they heard these things, he added and spake a parable, because he was nigh to Jerusalem, and because they thought that the kingdom of God should immediately appear. (Luke 19:11)
31So likewise ye, when ye see these things come to pass, know ye that the kingdom of God is nigh at hand. (Luke 21:31).
Paul preached the "kingdom of God"; that is, Paul preached the moral character of the kingdom, exhorting those who believed the gospel to walk worthy of God who had called them to His kingdom and glory. (1 Thess. 2:1212That ye would walk worthy of God, who hath called you unto his kingdom and glory. (1 Thessalonians 2:12).)
The eternal state will witness its true character in full display. "God all in all" means that the true character of God will be seen in the whole of new creation.
How blessed and glorious that eternity of rest!
O TEACH us more of Thy blest ways,
Thou holy Lamb of God!
And fix and root us in Thy grace,
As those redeemed by blood.
O tell us often of Thy love,
Of all Thy grief and pain;
And let our hearts with joy confess
That thence comes all our gain.
For this, O may we freely count-
Whate'er we have but loss;
The dearest object of our love,
Compared with Thee, but dross.
Engrave this deeply on our hearts
With an eternal pen,
That we may, in some small degree,
Return Thy love again.