Who is the 'ONE' who sits on the throne?

This has nothing to do with the topic under discussion which is the throne of God in Heaven.

Not at all, but I am saying the Father, the Son and the Holy Spirit are One.

Yes.

Jesus is the Word.

What is in the right hand of the One sitting?

Revelation 5:1
"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."

The Word of God is in his right hand.

Two possibilities...

Rainbow as Holy Spirit
Revelation 4:3
"And he that sat was to look upon like a jasper and a sardine stone: and there was a rainbow round about the throne, in sight like unto an emerald."

Seven Spirits
Revelation 4:5
"And out of the throne proceeded lightnings and thunderings and voices: and there were seven lamps of fire burning before the throne, which are the seven Spirits of God."

Who is the Father?

Romans 4:16
"Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all"

Who is the Slain Lamb?

Galatians 3:16
"Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ."

And yet, God is invisible...

Colossians 1:15
"Who is the image of the invisible God, the firstborn of every creature"

And a Consuming Fire...

Hebrews 12:29
"For our God is a consuming fire."

Is that what is being described in the Throne Room? Is God invisible and burning and consuming everything in the Throne Room?

Or does God exist *outside* of the Throne Room as well?

Zechariah 2:5
"For I, saith the LORD, will be unto her a wall of fire round about, and will be the glory in the midst of her."

How can God be both inside and outside at the same time?

Please read the accounts where God is shown on His throne.

Please read the accounts where God is invisible and a Consuming Fire.

No man has seen the Father, however man has seen Him incarnate as the Only Begotten Son.
"I and the Father are One."

Hint...

John 1:1
"In the beginning was the Word, and the Word was with God, and the Word was God."

God ultimately exists in a Higher Dimension... beyond the Throne Room folks.

It is a place where the Invisible Word 'frames' that which can be seen...

Hebrews 11:3 (Douay-Rheims Bible)
By faith we understand that the world was framed by the word of God; that from invisible things visible things might be made.

Thus, the 'visible' Throne Room is being made from the 'invisible' Word of God and the Consuming Fire.

This 'Highest Heaven' is where the 'Three' exist as 'One'. Remember, Information is invisible.

How can One see the information that is currently manifesting our reality?

Perhaps if we had Neo's special sunglasses...

Revelation 7:17
For the Lamb in the center of the throne will be their shepherd, and will guide them to springs of the water of life; and God will wipe every tear from their eyes.”

The book of Revelation is in his right hand. Signified by the seven trumpets of judgement

Jesus Christ is the one who sits on the throne he is the king of kings and the Lord of lords he would not be standing or sitting next to someone else on the throne he is the king of kings.

That "someone else" happens to be God the Father. So be careful what you say.

Why would the Book of Revelation be sealed if we can read it now?

Revelation 22:10
"And he saith unto me, Seal not the sayings of the prophecy of this book: for the time is at hand."

Interesting verse...

1 Timothy 6:16
"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."

That does not sound like the One sitting on the throne now does it.

In Revelation 5:1, the scroll is described as being written on both sides and sealed with seven seals. This suggests that the scroll contains a complete and comprehensive plan of salvation. The seven seals represent the seven barriers that must be overcome before the plan can be fully implemented.

Let me say it a better way 1 Kings 8:27:

"But will God indeed dwell on the earth? Behold, heaven and heaven of heavens cannot contain thee; how much less this house that I have builded!"

In this verse, Solomon is dedicating the temple he has built to God. He is acknowledging that God is so great and so powerful that not even the heavens can contain Him. How much less, then, can this house that Solomon has built contain Him? If the invisible God could look into a mirror His reflection would be Jesus Christ.
Colossians 1:15: "He (being Jesus) is the image of the invisible God, the firstborn over all creation." He cannot sit on a throne without a physical body which is Christ. Hope that helps in what I was trying to say

It does not say that plus the passage shows Jesus approaching the one on the throne and taking that book.

FALSE. We cannot substitute God the Son for God the Father. Therefore you are incorrect in what you have said.

Now kindly pay close attention to the Word of God -- the revelation of God given to us:
And immediately I was in the spirit: and, behold, a throne was set in heaven, and one sat on the throne. And he that sat was to look upon like a jasper and a sardine stone: and there was a rainbow round about the throne, in sight like unto an emerald... 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.

And I saw a strong angel proclaiming with a loud voice, Who is worthy to open the book, and to loose the seals thereof? And no man in heaven, nor in earth, neither under the earth, was able to open the book, neither to look thereon. And I wept much, because no man was found worthy to open and to read the book, neither to look thereon.

And one of the elders saith unto me, Weep not: behold, the Lion of the tribe of Juda, the Root of David, hath prevailed to open the book, and to loose the seven seals thereof. 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. And he came and took the book out of the right hand of him that sat upon the throne. (Rev 4:2,3; 5:1-7)

Now who is it who was seen sitting on the throne and in whose right hand was a book (scroll) with seven seals? Was that not GOD THE FATHER?

And who is the one who is the Lion of the tribe of Judah, the Root of David, the one who "CAME AND TOOK THE BOOK OUT OF THE RIGHT HAND OF HIM THAT SAT ON THE THRONE? Is that not the Lord Jesus Christ? Then why are you substituting the Son for the Father? Do you not believe God?

Scripture reveals Jesus is BOTH the Root and the Offspring of David; "I Jesus have sent mine angel to testify unto you these things in the churches. I am the root and the offspring of David,..." Rev 22:16

Insight from Isaiah 43:9-11: "Ye are my witnesses, saith the LORD, and my servant whom I have chosen: that ye may know and believe me, and understand that I am he: before me there was no God formed, neither shall there be after me.

I, even I, AM THE LORD; and BESIDE ME THERE IS NO SAVIOUR.

I have declared, and have saved, and I have shewed, when there was no strange god among you: therefore ye are my witnesses, saith the LORD, that I am God.
Yea, before the day was I am he; and there is none that can deliver out of my hand: I will work, and who shall let it?
Thus saith the LORD, YOUR REDEEMER, the Holy One of Israel; For your sake I have sent to Babylon, and have brought down all their nobles, and the Chaldeans, whose cry is in the ships.

I AM THE LORD, YOUR HOLY ONE, THE CREATOR OF ISRAEL, YOUR KING." Isa 43:10-15

The Revelation of Jesus Himself:
Rev 1:8
I am Alpha and Omega, the beginning and the ending, saith the Lord,

Rev 22:13
I am Alpha and Omega, the beginning and the end, the first and the last.

Rev 22:16
I Jesus have sent mine angel to testify unto you these things in the churches. I AM THE ROOT AND OFFSPRING of David, and the bright and morning star.