I believe it is you who have jumped ahead in prophecy concerning Christ and His kingdom. It is future. He is not on the throne right now. He is seated beside the one who is, God the Father.
Revelation 5 (future prophecy)
1 And I saw in the right hand of him that sat on the throne a book written within and on the backside, sealed with seven seals.
2 And I saw a strong angel proclaiming with a loud voice, Who is worthy to open the book, and to loose the seals thereof?
3 And no man in heaven, nor in earth, neither under the earth, was able to open the book, neither to look thereon.
4 And I wept much, because no man was found worthy to open and to read the book, neither to look thereon.
5 And one of the elders saith unto me, Weep not: behold, the Lion of the tribe of Judah, the Root of David, hath prevailed to open the book, and to loose the seven seals thereof.
6 And I beheld, and, lo, in the midst of the throne and of the four beasts, and in the midst of the elders, stood a Lamb as it had been slain, having seven horns and seven eyes, which are the seven Spirits of God sent forth into all the earth.
7 And he came and took the book out of the right hand of him that sat upon the throne.
Jesus Christ, the Lamb, came and took the book out of the right hand of him that sat upon the throne. Who is on the throne? God the Father. Jesus is not the one on the throne yet.
Revelation 7:10 And cried with a loud voice, saying, Salvation to our God which sitteth upon the throne, and unto the Lamb.
Again, the Father is on the throne and the Lamb is beside Him.
Hebrews 1
2 Hath in these last days spoken unto us by his Son, whom he hath appointed heir of all things, by whom also he made the worlds;
3 Who being the brightness of his glory, and the express image of his person, and upholding all things by the word of his power, when he had by himself purged our sins, sat down on the right hand of the Majesty on high:
4 Being made so much better than the angels, as he hath by inheritance obtained a more excellent name than they.
Jesus Christ is seated at the right hand of the Father. Jesus Christ has been appointed heir of all things. Jesus Christ is not yet taken hold of all things. It is a future prophecy.
Matthew 25
31 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:
32 And before him shall be gathered all nations: and he shall separate them one from another, as a shepherd divideth his sheep from the goats:
33 And he shall set the sheep on his right hand, but the goats on the left.
34 Then shall the King say unto them on his right hand, Come, ye blessed of my Father, inherit the kingdom prepared for you from the foundation of the world:
This is the future prophecy concerning Christ when He comes as King.