The kingdom of God is on earth for the following reasons:
1. God made the earth to be inhabited:
Isaiah 45:18 For thus saith the LORD that created the heavens; God himself that formed the earth and made it; he hath established it, he created it not in vain, he formed it to be inhabited: I am the LORD; and there is none else.
2. God intends to fill the earth with his glory:
Numbers 14:21 But as truly as I live, all the earth shall be filled with the glory of the LORD.
Habakkuk 2:14 For the earth shall be filled with the knowledge of the glory of the LORD, as the waters cover the sea.
3. God promised Abraham eternal inheritance of the land of Canaan, the land through which he walked:
Genesis 13:14 And the LORD said unto Abram, after that Lot was separated from him, Lift up now thine eyes, and look from the place where thou art northward, and southward, and eastward, and westward: 15 For all the land which thou seest, to thee will I give it, and to thy seed for ever. 16 And I will make thy seed as the dust of the earth: so that if a man can number the dust of the earth, then shall thy seed also be numbered. 17 Arise, walk through the land in the length of it and in the breadth of it; for I will give it unto thee.
Abraham didn’t receive the inheritance in his lifetime:
Acts 7:5 And he gave him none inheritance in it, no, not so much as to set his foot on: yet he promised that he would give it to him for a possession, and to his seed after him, when as yet he had no child.
To receive it he must be raised from the dead and the land must be there for him to inherit it.
4. God promised David a descendent who would sit upon his throne forever:
1 Chronicles 17:11 And it shall come to pass, when thy days be expired that thou must go to be with thy fathers, that I will raise up thy seed after thee, which shall be of thy sons; and I will establish his kingdom. 12 He shall build me an house, and I will stablish his throne for ever. 13 I will be his father, and he shall be my son: and I will not take my mercy away from him, as I took it from him that was before thee: 14 But I will settle him in mine house and in my kingdom for ever: and his throne shall be established for evermore.
5. Jesus Christ is the promised descendent who will sit upon David’s throne:
Luke 1:32 He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the throne of his father David: 33 And he shall reign over the house of Jacob for ever; and of his kingdom there shall be no end.
David’s throne was the throne of the Lord at the time when David and Solomon reigned.
1 Chronicles 29:23 Then Solomon sat on the throne of the LORD as king instead of David his father, and prospered; and all Israel obeyed him.
It will be restored as the throne of the Lord (YHWH) when Christ returns:
Jeremiah 3:17 At that time they shall call Jerusalem the throne of the LORD; and all the nations shall be gathered unto it, to the name of the LORD, to Jerusalem: neither shall they walk any more after the imagination of their evil heart.
6. We are told to pray for God’s kingdom to come; that his will might be done on earth:
Matthew 6:10 Thy kingdom come. Thy will be done in earth, as it is in heaven.
7. God’s kingdom will be ruled from Jerusalem:
Isaiah 2:2 And it shall come to pass in the last days, that the mountain of the LORD’S house shall be established in the top of the mountains, and shall be exalted above the hills; and all nations shall flow unto it. 3 And many people shall go and say, Come ye, and let us go up to the mountain of the LORD, to the house of the God of Jacob; and he will teach us of his ways, and we will walk in his paths: for out of Zion shall go forth the law, and the word of the LORD from Jerusalem. 4 And he shall judge among the nations, and shall rebuke many people: and they shall beat their swords into plowshares, and their spears into pruninghooks: nation shall not lift up sword against nation, neither shall they learn war any more.
8. There will be a mortal population:
Isaiah 65:20 There shall be no more thence an infant of days, nor an old man that hath not filled his days: for the child shall die an hundred years old; but the sinner being an hundred years old shall be accursed.
9. There will be a change in the behaviour of carnivores.
Isaiah 11:7 And the cow and the bear shall feed; their young ones shall lie down together: and the lion shall eat straw like the ox. 8 And the sucking child shall play on the hole of the asp, and the weaned child shall put his hand on the cockatrice’ den. 9 They shall not hurt nor destroy in all my holy mountain: for the earth shall be full of the knowledge of the LORD, as the waters cover the sea.
10. When Christ returns there will be an earthquake which will change the topography of the land of Israel:
Zechariah 14:4 And his feet shall stand in that day upon the mount of Olives, which is before Jerusalem on the east, and the mount of Olives shall cleave in the midst thereof toward the east and toward the west, and there shall be a very great valley; and half of the mountain shall remove toward the north, and half of it toward the south… 8 And it shall be in that day, that living waters shall go out from Jerusalem; half of them toward the former sea, and half of them toward the hinder sea: in summer and in winter shall it be. 9 And the LORD shall be king over all the earth: in that day shall there be one LORD, and his name one. 10 All the land shall be turned as a plain from Geba to Rimmon south of Jerusalem: and it shall be lifted up, and inhabited in her place, from Benjamin’s gate unto the place of the first gate, unto the corner gate, and from the tower of Hananeel unto the king’s winepresses. 11 And men shall dwell in it, and there shall be no more utter destruction; but Jerusalem shall be safely inhabited.
11. A new sanctuary will be built in the land as prophesied in Ezekiel:
Ezekiel 37:26 Moreover I will make a covenant of peace with them; it shall be an everlasting covenant with them: and I will place them, and multiply them, and will set my sanctuary in the midst of them for evermore. 27 My tabernacle also shall be with them: yea, I will be their God, and they shall be my people. 28 And the heathen shall know that I the LORD do sanctify Israel, when my sanctuary shall be in the midst of them for evermore.
12. A river will flow from the new Temple; and the dead sea will be healed by the waters that flow into it:
Ezekiel 47:1 Afterward he brought me again unto the door of the house; and, behold, waters issued out from under the threshold of the house eastward: for the forefront of the house stood toward the east, and the waters came down from under from the right side of the house, at the south side of the altar. 2 Then brought he me out of the way of the gate northward, and led me about the way without unto the utter gate by the way that looketh eastward; and, behold, there ran out waters on the right side… 8 Then said he unto me, These waters issue out toward the east country, and go down into the desert, and go into the sea: which being brought forth into the sea, the waters shall be healed.
13. The tribes of Israel will be resettled in the land of Canaan as prophesied in Ezekiel 48.
14. The faithful will inherit the earth:
Psalms 37:9 For evildoers shall be cut off: but those that wait upon the LORD, they shall inherit the earth.
Psalms 37:11 But the meek shall inherit the earth; and shall delight themselves in the abundance of peace.
Psalms 37:22 For such as be blessed of him shall inherit the earth; and they that be cursed of him shall be cut off.
Matthew 5:5 Blessed are the meek: for they shall inherit the earth.
New heavens and a new earth
When we read of a new heavens and a new earth, we are not to suppose that the existing heaven and earth are to be literally destroyed and replaced.
2 Peter 3:10 But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up. 11 Seeing then that all these things shall be dissolved, what manner of persons ought ye to be in all holy conversation and godliness, 12 Looking for and hasting unto the coming of the day of God, wherein the heavens being on fire shall be dissolved, and the elements shall melt with fervent heat? 13 Nevertheless we, according to his promise, look for new heavens and a new earth, wherein dwelleth righteousness.
Peter is using a metaphor to describe the complete removal of man’s government, man-made religions and institutions, to be replaced by Christ’s government and the knowledge of true righteousness.
The arrangement is described as new heavens and a new earth
Isaiah 65:17 For, behold, I create new heavens and a new earth: and the former shall not be remembered, nor come into mind. 18 But be ye glad and rejoice for ever in that which I create: for, behold, I create Jerusalem a rejoicing, and her people a joy. 19 And I will rejoice in Jerusalem, and joy in my people: and the voice of weeping shall be no more heard in her, nor the voice of crying... 21 And they shall build houses, and inhabit them; and they shall plant vineyards, and eat the fruit of them. 22 They shall not build, and another inhabit; they shall not plant, and another eat: for as the days of a tree are the days of my people, and mine elect shall long enjoy the work of their hands.
Isaiah 66:22 For as the new heavens and the new earth, which I will make, shall remain before me, saith the LORD, so shall your seed and your name remain.
Similarly in Revelation:
Revelation 21:1 And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea.
Revelation 21:5 And he that sat upon the throne said, Behold, I make all things new. And he said unto me, Write: for these words are true and faithful.
The words are used symbolically to describe a new order of things, not the replacement of the literal heaven and earth.
The absence of the sea is not the literal sea. It represents the absence of wickedness in the nations warring with one another.
Isaiah 57:20 But the wicked are like the troubled sea, when it cannot rest, whose waters cast up mire and dirt.
We know this because Christ is promised dominion from sea to sea.
Psalms 72:8 He shall have dominion also from sea to sea, and from the river unto the ends of the earth.
This reign of Christ over the mortal population will last 1000 years.
This will be followed by a second resurrection and final judgment. Sin and death will be eradicated and God will be ‘all in all’.
Paul explains what is going to happen:
1 Corinthians 15:22 For as in Adam all die, even so in Christ shall all be made alive. 23 But every man in his own order: Christ the firstfruits; afterward they that are Christ’s at his coming. 24 Then cometh the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power. 25 For he must reign (the millennial reign), till he hath put all enemies under his feet. 26 The last enemy that shall be destroyed is death. 27 For he hath put all things under his feet. But when he saith all things are put under him, it is manifest that he is excepted, which did put all things under him. 28 And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all.
No one other than Jesus Christ has ever gone to heaven.
John 3:13 And no man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven.
The kingdom of God is the restored kingdom of David upon the earth.
May I suggest that you read:
The Kingdom of God on Earth (click on title)
Also The Kingdom of Heaven on Earth (click on title)
I hope you find this helpful.