How in the world can anyone deny that this verse is speaking of an earthly kingdom?:
"After this manner therefore pray ye: Our Father which art in heaven, Hallowed be thy name. Thy kingdom come, Thy will be done in earth, as it is in heaven" (Mt.6:9-10).
Of course the Lord is telling His disciples to pray for the kingdom to come to the earth. And when it does come to the earth then the Lord's "will" will be done on the earth.
So it is evident that the kingdom spoken of in this verse is speaking about an earthly kingdom.
Jesus said the His Kingdom was not of this world, so how can it be an earthly Kingdom?
Then why does the Lord Jesus say that He will not sit upon His throne until He returns to the earth?:
"When the Son of man shall come in his glory, and all the holy angels with him, then shall he sit upon the throne of his glory" (Mt.25:31).
It's important to look at the whole of Scripture, not take one verse and define one's beliefs on it. Jesus is reigning and ruling NOW. He is called King now. He will eventually, in the world to come, reign on His throne in view of all.
Romans 14:17
for the kingdom of God is not meat and drink; but righteousness, and peace, and joy in the Holy Ghost.
1 Corinthians 15:50
Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God; neither doth corruption inherit incorruption.
Colossians 1:13
who hath delivered us from the power of darkness, and hath translated us into the kingdom of his dear Son:
1 Tim 1
16 Howbeit for this cause I obtained mercy, that in me first Jesus Christ might shew forth all longsuffering, for a pattern to them which should hereafter believe on him to life everlasting. 17 Now unto the King eternal, immortal, invisible, the only wise God, be honour and glory for ever and ever. Amen.
1 Tim 6
14 that thou keep this commandment without spot, unrebukeable, until the appearing of our Lord Jesus Christ: 15
which in his times he shall shew, who is the blessed and only Potentate, the King of kings, and Lord of lords; 16 who only hath immortality, dwelling in the light which no man can approach unto; whom no man hath seen, nor can see: to whom be honour and power everlasting. Amen.
Hebrews 1:8
But unto the Son he saith, Thy throne, O God, is for ever and ever: a sceptre of righteousness is the sceptre of thy kingdom.
Hebrews 7:1
For this Melchisedec, king of Salem, priest of the most high God, who met Abraham returning from the slaughter of the kings, and blessed him; 2to whom also Abraham gave a tenth part of all; first being by interpretation King of righteousness, and after that also King of Salem, which is, King of peace;
Heb 12
27 And this word, Yet once more, signifieth the removing of those things that are shaken, as of things that are made, that those things which cannot be shaken may remain. 28 Wherefore we receiving a kingdom which cannot be moved, let us have grace, whereby we may serve God acceptably with reverence and godly fear: 29 for our God is a consuming fire.
Revelation 1:9
I John, who also am your brother, and companion in tribulation, and in the kingdom and patience of Jesus Christ, was in the isle that is called Patmos, for the word of God, and for the testimony of Jesus Christ.
Revelation 11:15
And the seventh angel sounded; and there were great voices in heaven, saying, The kingdoms of this world are become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever.
Revelation 15:3
And they sing the song of Moses the servant of God, and the song of the Lamb, saying, Great and marvellous are thy works, Lord God Almighty; just and true are thy ways, thou King of saints.
Revelation 17:14
These shall make war with the Lamb, and the Lamb shall overcome them: for he is Lord of lords, and King of kings: and they that are with him are called, and chosen, and faithful.
Revelation 19:16
And he hath on his vesture and on his thigh a name written, KING OF KINGS, AND LORD OF LORDS.