Let's elaborate on the idea of One Kingdom.
The Kingdom of Heaven is a Biblical concept referring to the realm governed by God. It is not Earth; it is not corrupted. It is the "good place" we go to after our death if we have repented and given ourselves to Jesus.
That sense of the Kingdom is our destination.
But we sometimes forget that Jesus also used the phrase as a metaphor for the community created here on Earth now by practicing Christians.
The kingdom of which Jesus spoke is, as Paul wrote, marked by “righteousness and peace and joy in the Holy Spirit” (Rom. 14:17). It exists in the hearts of all those in whom the King lives. The wonder of wonders is that the Trinity takes up residence in the hearts of those who embrace Christ and enter the spiritual kingdom. In John 14:17 Jesus promised that the Holy Spirit would indwell believers, while in verse 23 He added, “If anyone loves Me, he will keep My word; and My Father will love him, and We will come to him and make Our abode with him.”
For the sake of guiding our activism and outreach today, we are talking about the Kingdom of Heaven in that second, metaphorical sense of living now as though we were all subjects of one King. To this end we focus on nondenominational, "back to basics" evangelism to introduce people to Jesus and Christian principles... and to stay clear about those principles ourselves.
We desire to engage in the world Christians first, everything else second.
Here are some other verses about the Kingdom of Heaven.
Then the sovereignty, power and greatness of all the kingdoms under heaven will be handed over to the holy people of the Most High. His kingdom will be an everlasting kingdom, and all rulers will worship and obey him.
He will judge between many peoples
and will settle disputes for strong nations far and wide.
They will beat their swords into plowshares
and their spears into pruning hooks.
Nation will not take up sword against nation,
nor will they train for war anymore.
and under their own fig tree,
and no one will make them afraid,
for the Lord Almighty has spoken.
Your kingdom is an everlasting kingdom,
and your dominion endures through all generations.
Jesus said, “My kingdom is not of this world. If it were, my servants would fight to prevent my arrest by the Jewish leaders. But now my kingdom is from another place.”
“You are a king, then!” said Pilate.
Jesus answered, “You say that I am a king. In fact, the reason I was born and came into the world is to testify to the truth. Everyone on the side of truth listens to me.”
Once, on being asked by the Pharisees when the kingdom of God would come, Jesus replied, “The coming of the kingdom of God is not something that can be observed, nor will people say, ‘Here it is,’ or ‘There it is,’ because the kingdom of God is in your midst.”